Effect of pulsed light treatment on the phytochemical, volatile, and sensorial attributes of lactic-acid-fermented mulberry juice

ABSTRACT

Lactic-acid-fermented mulberry juice (LFMJ) was subjected to pulsed light (PL) treatment at exposure time of 2, 4, and 8 s at high insensitive pulses of 14.0 J/cm². The effect of PL treatment on the microbial inactivation, physicochemical, phytochemical, volatile, and sensory characteristics of LFMJ was evaluated. It was found that the PL was able to reduce the microbial load to acceptable levels (1.02 ± 0.04 log₁₀ cfu/mL) with no significant impact on the physicochemical properties of LFMJ. It was also observed that the PL treatment caused a slight decrease in anthocyanin concentration at 8 s exposure time. The color difference (∆E) of the juice treated for 2 and 4 s fell below the slightly noticeable range 0.5<ΔE<1.5 while ∆E values for the 8 s (0.55 ± 0.02) and the thermal (0.50 ± 0.02) treated samples were slightly noticeable. The volatile profile and odor activity values were positively affected by increasing the exposure time. The results depict that, under the present experimental conditions, the application of the PL resulted in a fermented juice with superior quality attributes as compared to the thermal treated juice.

KEYWORDS:

• Fermentation
• Influence
• Lactic acid bacteria
• Mulberry
• Pasteurization
• Pulsed light

Introduction

Mulberry is a monoecious plant cultivated in Africa, Asia, Europe, South America, and North America.^[1] It belongs to the genus Morus from the Moraceae family. There are 24 species of Morus and one subspecies, with at least 100 known varieties.^[2] The fruit has been extensively used in traditional medicine in treating ailments such as malaria, diabetes, hepatitis, dermatitis, atherosclerosis, asthma, and rheumatism.^[3] Besides, it is regarded as a nutritious food that varies according to variety, environmental factors, and geographical location.^[4] The fruit is very perishable^[5] hence the need to preserve it from postharvest loss. To address this challenge, the fruit is often processed into fruit jellies, jam, wines, and nonalcoholic beverage, among others.^[6,7]

To date, the application of conventional thermal processing of fruit juices remains the most common technique for preservation and shelf-life extension of fruit juice because of its ability to inactivate microorganisms and spoilage enzymes. However, heat processing particularly under certain conditions have been reported to induce detrimental effect on the nutritional, phytochemical, and sensory qualities of food^[8–10] as well as reducing the content or bioavailability of some bioactive compounds.^[9,11] Consumer’s demand for nutritious, natural, and healthier foods, which are minimally and naturally processed makes it imperative for food manufacturers to explore various technologies that impact less on the quality of processed foods. This has necessitated the need for exploration into novel nonthermal pasteurization technologies such as high hydrostatic pressure, pulsed electric fields, pulsed magnetic field, pulsed light, and ultrasonication, among others, to complement or replace the conventional heat pasteurization techniques.^[12,13] Besides, these novel technologies are not only employed to maintain the quality of foods but also to enhance their functionality.

Pulsed light (PL) is a novel nonthermal technology that encompasses the use of short duration (1 µs–0.1 s) penetrating pulses with broad spectrum comparable to that of sunlight, including not only ultraviolet light but also visible and near infrared radiation (200–1100 nm) to guarantee the safety of foods as the results of its photochemical effect on microbial cell physiology.^[14,15] The high-energy pulses cause structural changes in proteins, DNA, membranes, and other cellular components of microorganisms. Studies have established the positive effect of PL on microbial safety of many foods.^[16] Pulse light has also been successfully used in the processing of orange juice,^[17] apple and cranberry juice blend,^[18] mushroom,^[14] sliced carrot,^[19,20] apple,^[21] fresh-cut mangoes,^[22] apple juice,^[17] and milk,^[17,23] among others, to enhance their quality and safety.

In spite of the potential of PL for commercial use in minimal processing of foods, no empirical study has been conducted to assess the effect of PL on volatile and sensory profile of food products, especially for mulberry. In view of the above, this study sought to investigate the effect of PL treatments on the phytochemicals, volatile, and sensorial qualities of lactic-acid-fermented mulberry juice.

Materials and methods

Materials

Pure volatile standards were purchased from Sigma-Aldrich (Shanghai, China), Tái wān 1 háo (Morus nigra) fruits were purchased from a farm in Zhenjiang, Jiangsu Province, China. The lactic acid bacteria (LAB) Lactobacillus plantarum (ATCC SD5209) was procured from DuPont China Holding Co. Ltd (Shanghai, China); whereas, pectinase enzyme (Pectinex UF) was obtained from Novozymes (Beijing, China). DeMan, Rogosa, and Sharpe (MRS) broth and MRS agar were acquired from Sigma-Aldrich (Shanghai, China). All other analytical grade chemicals were purchased from Sinopharm Chemical Reagent Co. Ltd (Shanghai, China).

Activation of starter culture

To activate the LAB, 0.01 g of it was cultured in 100 mL of MRS broth for 18 h at 37°C and sub-cultured twice in MRS broth at 35°C for 24 h each. Thereafter, the culture was centrifuged (Anke KA—1000) at 3500 rpm and 4°C for 10 min. Microbial cells were harvested, washed with 0.1% sterile NaCl and cell concentration (10⁵ cfu/mL) determined using hemocytometer version XB-K-250 (Jianling Medical Device Co., Danyang, China).

Beverage formulation and fermentation

Mulberry fruits were rinsed with 0.02% sodium hypochlorite and sterile water to eliminate surface microbial load. The disinfected fruits were crushed using a household blender (Hurom slow juicer, Los Angeles, USA). Two grams of ascorbic acid was added to 2 kg of the Must and clarified using Pectinex UF enzyme (0.010% v/w) at 45°C for 1 h. The juice was centrifuged (Avanti J-26 XP Beckman Coulter, Inc., Brea, CA) at 4°C, for 10 min at 8000 rpm. Based on the optimum lactic acid fermentation conditions established by Kwaw et al.,^[7] the brix of the juice was adjusted to 14.00 and pH adjusted to 4.00. After the adjustments, 200 mL of the sample was inoculated with 3.90% v/v inoculum (L. plantarum) and incubated at 40°C in a rotary incubator (IS-RDD3, Crystal Technology and Industries, Jiangsu, China) for 36 h at 100 rpm.

Microbiological enumeration

The microbial assay for the fermented samples was performed using the plate count method described by Donsì et al.^[13] with slight modifications. Briefly, ten-fold dilution series of samples were prepared using sterile distilled water and 0.1 mL aliquots of appropriate dilutions pour plated using plate count agar (PCA). Plates were incubated at 37°C for 36 h, and colony forming units (CFU)/mL were estimated.

Pulse light treatment

Pulsed light (PL) treatment was carried out using RS-3000B Steripulse-XL system (Xenon Corporation, Wilmington, MA, USA) as described by Palgan et al.^[17] with slight modifications. The sample was dispensed into petri dishes (100 mm diameter) to ensure that the entire dish surface was covered with the sample to a depth of 1 mm. To minimize temperature increases of the samples, petri dishes containing the samples were cooled to 3°C and positioned on a stainless-steel shelf located at 2.5 cm of vertical distance from the quartz window of the Xenon flash lamp (Model No. RC 747, Xenon Corporation MA, USA). To reduce differences in radiation dose absorption, the samples were placed within a uniform area of the radiation field. Light pulses were delivered at a pulse width of 360 µs, frequency of 3 Hz, and delivering radiant energy of 1.17 J/cm²/pulse. The samples were exposed to a high intensity light pulse of 14 J/cm² for 2, 4, and 8 s.

Thermal treatment

The thermal pasteurization was carried out as described by Caminiti et al.^[24] with modifications. Briefly, the tubular heat exchanger (Model No. FT74T, Armfield, Ringwood, UK) was thoroughly cleaned according to the manufacturer’s instructions. Thereafter, the juice was pasteurized at a flow rate of 94 mL/min with the temperature of the holding tube set at 72°C, a residence time of 26 s, and a come-up time of 3.5 min. All other important parameters were monitored using the equipment’s logging system.

pH titratable acidity and total soluble solids

Total soluble solids (TSS) were determined using a digital refractometer (Beijing Yaxingtai Electrical Equipment, Beijing, China). The pH of the samples was measured using LIDA Instrument PHS-3C Precision pH/mV meter (LIDA Instrument, Shanghai, China). Titratable acidity (TA) was determined using the method described by Bhat et al.^[25] with some modifications. Briefly, 3.0 g of the sample was allotted in a 200.0 mL beaker after which 30.0 mL distilled water was added. Using phenolphthalein as an indicator, the mixture was titrated against a standardized 0.1 N NaOH. The total acidity in gram of lactic acid per liter of the juice was calculated using the following equation (Eq. 1):

(1) $\mathrm{T}\mathrm{A}=\frac{\mathrm{v}\times 0.1\mathrm{N}\mathrm{N}\mathrm{a}\mathrm{O}\mathrm{H}\times \mathrm{z}}{\mathrm{m}}$(1)

where v is the titer value of NaOH, z is milliequivalent weight of lactic acid (0.09), and m is the mass of the sample.

Total phenolics concentration

Total phenolic concentration (TPC) was estimated using the Folin–Ciocalteu method described by Aydın et al.^[26] with some modifications. A 2 mL freshly prepared Folin–Ciocalteu reagent (1:1 v/v) and 2 mL of sodium carbonate (75 g·L⁻¹) were added to 0.2 mL of the sample in a test tube, and vortexed for 60 s. The mixture was incubated at 25°C for 30 min, and the absorbance was read at 760 nm using UV spectrophotometer (UV-1600, Beijing Rayleigh analytical instrument, Beijing, China). The TPC was expressed in terms of milligrams of gallic acid equivalent per milliliter of juice.

Total anthocyanin concentration

The total anthocyanin concentration (TAC) was determined by the pH differential method described by Kwaw et al.^[7] Two buffer solutions: CH₃COONa (0.4 mol·L⁻¹) at pH 4.5 and KCl (0.25 mol·L⁻¹) at pH 1 were prepared. A 0.1 mL each of the sample was dispensed into two sets of tubes. One set of the sample was adjusted to 10 mL with the KCl buffer while the other set was adjusted with the CH₃COONa. The tubes were vortex, and their absorbances were read at 510 nm and 700 nm using UV spectrophotometer (UV-1600) against a blank (water and reagents). The TAC was calculated using Eq. (2) and expressed as milligrams equivalent of cyanidin 3-glucoside per milliliter of the juice.

(2) $TAC=\hspace{0.17em}\left[\left(A_1-A_2\right)-\left(A_3-A_4\right)\right]\times \frac{MW\times DF\times {10}^2}{\times L}$(2)

where A₁ is the absorbance at 510 nm at pH 1.0, A₂ is the absorbance at 700 nm at pH 1.0, A₃ is the absorbance at 510 nm at pH 4.5, A₄ is the absorbance at 700 nm at pH 4.5, and MW is the molecular weight of cyanidin-3-glucoside (449.2 g·mol⁻¹); DF is the dilution factor (100); L is the path length (1 cm); ɛ is the molar extinction coefficient for cyanidin-3-glucoside (26,900 L·mol⁻¹·cm)

Total flavonoid concentration

The aluminum chloride colorimetric method as described by Tchabo et al.^[27] with slight modifications was employed in the determination of the total flavonoid concentration (TFC) of the juice. Briefly, 0.3 mL NaNO₂ (50 g/L) and 4 mL distilled water were added to the sample (1 mL) and vortexed for 60 s. The mixture was allowed to stand for 5 min after which 1 mL of AlCl₃ (100 g/L) was added, vortexed, and allowed to stand. After 5 min, 2 mL of NaOH (1 mol/L) was added and the final volume was adjusted to 10 mL with 2.4 mL distilled water. The mixture was incubated at 25°C for 10 min with 2 min periodic vortexing (15 s). Thereafter, the absorbance was read at 510 nm using UV spectrophotometer (UV-1600). The TFC was expressed as milligrams of rutin equivalents per milliliter of the juice.

Volatile compounds and odor activity analysis

The headspace gas chromatography–mass spectrometry method was used in the analysis of the volatile compounds. The odor activity value (OAV) for each volatile component was valued by dividing its concentration by the odor threshold.^[28]

Solid-phase microextraction

The headspace solid-phase microextraction (HS-SPME) method described by Qin et al.^[29] with slight modification was used in the extraction of the volatile compounds. Briefly, 1.5 g NaCl was added to 5 mL of sample in a 15.0 mL glass vial. Thereafter, 2-octanol (10 µL, 800 µg/L) was added to the mixture, which was vial sealed with silicone septum and the mixture equilibrated for 20 min at 40°C. The DVB/CAR/PDMS fiber (50/30 μm) (Supelco, Pennsylvania, USA) was exposed to the headspace of the vial with continuous stirring at 750 rpm. After 30 min, the fiber was removed and desorption was carried out at 250°C for 5 min by introducing fiber into the injection port of the Agilent 6890N-5973B gas chromatograph (GC) coupled with a mass spectrometer detector (MSD).

Gas chromatography analysis

The volatile compounds were separated on Agilent J&W DB-WAX GC column, 60 m × 0.25 mm × 0.25 μm film thickness (Beijing, China). The chromatographic analysis was carried out as described by Butkhup et al.^[30] with some modifications. The chromatographic conditions were as follows: Injection mode (splitless), carrier gas (He at 1 mL/min), injection temperature (250°C), detector temperature (250°C), mass spectrometry (MS) scan range (33–350 amu), temperature program (50°C for 10 min, increased to 150°C at 6°C/min, then raised to 200°C at 8°C/min and held for 7 min), source temperature (230°C), energy (70 eV), and quadrupole (150°C).

Identification and semi-quantification of volatile compounds

The identification of the volatile components was carried out by comparing their GC retention times with those of pure standards carried out under the same chromatographic conditions and their mass spectra with those in library databases (Wiley Spectral Library and NIST Library 2005 v 2.0). Series of n-alkanes (C5-C25) (Sigma-Aldrich) were run under the same conditions and used in calculating the linear retention indices (RI) of the compounds.^[31]

Color assessment

Color measurement of CIE parameters (L*, a*, and b*) as described by Fazaeli et al.^[32] using Hunter colorimeter model color Quest XE (HunterLab, Reston, USA) was carried out on the samples. The total color difference (ΔE) was calculated as [(${\mathrm{L}}_{\mathrm{O}}^{\ast }$ – L*)² + (a_o -a*)² + (b_o -b*)²] ^½, the chroma (C) as (a^*2 + b^*2)^1/2, and the hue angle (H°) as tan⁻¹(b*/a*). ${\mathrm{L}}_{\mathrm{o}}^{\ast },{\mathrm{a}}_{\mathrm{o}}^{\ast }{,\mathrm{a}\mathrm{n}\mathrm{d}\mathrm{b}}_{\mathrm{o}}^{\ast }$ are the untreated mulberry juice chromatic values obtained for brightness, red/green, and yellow/blue; whereas, L*, a*, and b* are the respective chromatic values for the treated samples.

Sensory evaluation

Sensory attributes (aroma, color, taste, flavor, mouthfeel, and overall acceptability) of the samples (FMJ, TFMJ, PFMJ-1, PFMJ-2, and PFMJ-3) were assessed using 45 semi-trained panelists (20 males and 25 females) made up of staff of the School of Food and Biological Engineering, Jiangsu University. The samples were randomly presented to the panelist in clear plastic cups (15.0 mL) with a 3-digit code number. Each panel evaluated the samples (10 mL) on a 9-point hedonic scale (1 = extremely dislike; 2 = very much dislike; 3 = dislike; 4 = slightly dislike; 5 = neither like nor dislike; 6 = slightly like; 7 = like; 8 = like very much; 9 = like extremely).^[33]

Statistical analysis

The results from the study were presented as mean ± standard deviation of three independent treatments and assays. The analysis of variance (ANOVA) was carried out using OriginPro version 2015 (OriginLab, Northampton, USA). Differences were considered to be significant at p < 0.05 (95% confidence level) using the Tukey test.

Results and discussions

Physicochemical and microbial analysis

The study (Table 1) showed no significant changes (p < 0.05) in the pH, brix, and titratable acidity of the treated samples regardless of the treatment applied compared to the LFMJ. Similar trends have been reported in the literature on juice subjected to PL treatments.^[17,18,34]

Table 1. Microbial assay and physicochemical properties of thermal and nonthermal treated lactic-acid-fermented mulberry juice.

	Microbial load (log Cfu/mL)	pH	Brix (°Bx)	TA (g/L of la)
LFMJ	7.62 ± 0.09^a	3.55 ± 0.04^a	9.08 ± 0.04^a	35.48 ± 1.13^a
TLFMJ	3.09 ± 0.06^b	3.49 ± 0.03^a	8.96 ± 0.06^b	35.47 ± 1.24^a
PLFMJ-1	2.16 ± 0.10^c	3.56 ± 0.04^a	8.98 ± 0.03^ab	35.20 ± 1.00^a
PLFMJ-2	1.20 ± 0.06^d	3.58 ± 0.05^a	8.96 ± 0.04^b	34.95 ± 1.02^a
PLFMJ-3	1.02 ± 0.04^e	3.58 ± 0.04^a	8.97 ± 0.03^ab	35.10 ± 0.95^a

Data expressed as mean ± standard deviation

LFMJ: lactic-acid-fermented mulberry juice; TLFMJ: thermal pasteurized fermented mulberry juice; PLFMJ: pulsed light pasteurized fermented mulberry juice (1 – 2 s; 2 – 4 s; 3 – 8 s)

TA: titratable acidity (g/L of lactic acid), la: lactic

Values in the same column with same superscripted alphabet shows no significant difference at p < 0.05

The counts of the estimated microorganism after the 36 h fermentation, thermal, and pulsed light treatments are presented in Table 1. The fermented mulberry juice (LFMJ) had 7.62 log CFU/mL, but the thermal treatment (TT) and pulsed light (PL) treatment significantly (p < 0.05) reduced the microbial load of the juice. However, the application of TT was less effective than the PL. Similar trends in microbial inactivation using PL have been reported in orange and apple juice.^[17] The foremost outcome on microbial inactivation produced by PL has been ascribed to the photochemical action of the UV radiation that modifies the structure of the DNA, impaired replication, and gene transcription.^[16] Besides, the release of energy from the numerous penetrating flashes per second that upsurges the rapid energy intensity also contributes to microbial inactivation.^[35] This was attested in the study with increasing exposure time resulting in a significant (p < 0.05) log reduction in microbial load of the juice (Table 1). This could be due to a progressive increase in the lethal effect that might have caused microbial cells inactivation. Other factors such as the food adsorption physiognomies or hypnotic power might have contributed to the level of inactivation with regard to the PL.^[36]

Phytochemical and color analysis

The results on the influence of PL on the phytochemical properties of the LFMJ are presented in Table 2. The results depicted a slight increase in the TPC and TFC of the LFMJ^[37] but a significant (p < 0.05) decrease in TAC of PLFMJ-3. The significant change in TAC of PLFMJ-3 could be due to adverse photochemical reactions that might have taken place with the exposure of the juice to the PL.^[38]

Table 2. Phytochemical and colorimetric properties of pulsed light treated lactic-acid-fermented mulberry juice.

Sample	TPC	TFC	TAC	L*	a*	b*	H°	C*	∆E
LFMJ	929.47 ± 3.49^a	438.17 ± 4.00^a	142.77 ± 2.50^a	4.06 ± 0.06^b	13.90 ± 0.28^a	5.37 ± 0.03^c	21.12 ± 0.17^e	14.90 ± 0.14^a
TLFMJ	801.12 ± 2.86^b	421.65 ± 3.61^b	128.72 ± 2.43^b	4.19 ± 0.01^a	13.47 ± 0.07^bc	5.54 ± 0.06^ab	22.36 ± 0.11^c	14.56 ± 0.09^a	0.48 ± 0.02^b
PLFMJ-1	931.30 ± 3.50^a	438.65 ± 2.00^a	140.50 ± 1.00^a	4.07 ± 0.02^b	13.86 ± 06^a	5.41 ± 0.05^c	21.32 ± 0.06^e	14.88 ± 0.15^a	0.06 ± 0.00^d
PLFMJ-2	932.10 ± 3.13^a	438.74 ± 3.10^a	140.20 ± 1.25^a	4.08 ± 0.02^b	13.80 ± 0.05^ab	5.48 ± 0.04^bc	21.66 ± 0.08^d	14.85 ± 0.08^a	0.15 ± 0.01^c
PLFMJ-3	932.45 ± 4.20^a	439.40 ± 3.00^a	133.54 ± 1.15^b	4.20 ± 0.01^a	13.43 ± 0.06^c	5.61 ± 0.05^a	22.67 ± 0.09^b	14.55 ± 0.08^a	0.55 ± 0.02^a

Data expressed as mean ± standard deviation

LFMJ: lactic-acid-fermented mulberry juice; TLFMJ: thermal pasteurized fermented mulberry juice; PLFMJ: pulsed light pasteurized fermented mulberry juice (exposure time of 1 – 2 s; 2 – 4 s; 3 – 4 s);

TPC: total phenolic concentration (mg/100 mL); TFC: total flavonoid concentration (mg/100 mL); TAC: total anthocyanin concentration (mg/100 mL); L* – lightness; a*: redness; b*: yellowness; C*: chroma; H°: hue angle; ∆E: color difference

Means that do not share a letter are significantly different at P < 0.05

The results on the color attributes (L*, a*, and b*) and the total color differences (∆E) as influenced by the PL are shown in Table 2. The lightness (L*) increased slightly as the exposure time increased (Table 2) but was only significant in PLFMJ-3 (8 s of treatment). This could be attributed to a decrease in monomeric anthocyanin concentration of the juice during the treatment.^[38,39] This confirms the significant negative correlation observed in Table 3 between TAC and L* (r = −0.936) that is in line with the findings of Wang et al.^[40]

Table 3. Pearson’s correlation coefficients of phytochemical and color properties of pulsed light treated lactic-acid-fermented mulberry juice.

	TPC	TFC	TAC	L*	a*	b*	H°	C*
TPC	1
TFC	0.999*	1
TAC	0.798	0.773	1
L*	−0.557	−0.523	−0.936*	1
a*	0.542	0.508	0.932*	−0.998*	1
b*	−0.319	−0.282	−0.809	0.926*	−0.945*	1
H°	−0.434	−0.398	−0.881*	0.975*	−0.985*	0.987*	1
C*	0.582	0.549	0.946*	−0.999*	0.998*	−0.921*	−0.972*	1

*Correlation significant at 0.05 level

TPC: total phenolic concentration; TFC: total flavonoid concentration; TAC: total anthocyanin concentration; L*: lightness, a*: redness; b*: yellowness; C*: chroma, H°: hue angle.

The study showed a slight decrease in b* values but the extent of the decrease was not significant (P < 0.05). It was observed that increasing the exposure time resulted in a slight decrease in a* and an increase in b* but were only significant (p < 0.05) in PLFMJ-3. The heat treatment (TLFMJ) on the other hand caused an increase in L* and b* that could be the result of the negative impact of thermal pasteurization on the phytochemical components.^[41] The ∆E values increased with increasing PL exposure time (Table 2) but the ∆E values for PLFMJ-1 and PLFMJ-2 fell below the slightly noticeable range 0.5<ΔE<1.5 according to the classification reported by Cserhalmi, et al.^[42] However, the ΔE for TLFMJ (0.50 ± 0.02) and PLFMJ-3 (0.55 ± 0.02) were slightly noticeable (Table 2). These noticeable color differences could be as a result of the heat in the case of TLFMJ and photochemical reactions (PLFMJ-3) that resulted in the degradation of TAC of those juices. Anthocyanins are mainly responsible for the color of mulberry,^[43] and hence TAC are associate with changes in L*, a*, and b*.^[44] The decrease in TAC (Table 2) led to a decrease in a* thus making the sample dark thereby an increase in L* (Table 2). This presupposes that the slight degradation of anthocyanins with increasing exposure time might have resulted in the formation of new polymeric complex hence, the upsurge in b* and a decline in a*.^[45,46] This confirms the significant positive correlation (r = 0.932) between TAC and a* and negative correlation (r = −0.936) between TAC and L* (Table 3). Besides, H° (Table 3) was found to be significantly negative correlated to TAC (r = −0.881), TFC (R = −0.967), and a* (r = −0.985) but positively correlated with L* (r = 0.975) and b* (r = 0.987). Meanwhile, C* was noted to be positively correlated with TAC (r = 0.946) and a* (r = 0.998) but negatively correlated with L* (r = −0.999), b* (r = −0.921), and H° (r = −0.972). These findings substantiate the notion that change in phytochemical components relates to CIE color components (a and b) as emphasized by H° and C*, which are quantitative and qualitative colorimetric information associated with color recognition by humans.^[44,46]

Changes in volatile compounds of pulsed light treated lactic-acid-fermented mulberry juice

The volatile compounds found in the mulberry juice samples are enumerated in Table 4. A total of 34, 55, and 36 volatile compounds comprising aldehydes, ketones, esters, alcohols phenols, furans, lactones, and acids with varying concentrations were determined in the RMJ, LFMJ, and TLFMJ samples respectively; whereas, 51 volatile compounds each were found in the PL treated samples (Table 4). The decrease in the number of volatile compounds after the PL occurred mostly in the ketones that could be due to photochemical reactions during the treatment. There were, however, increments in the concentrations of the volatile compounds with increasing exposure time (PLFMJ-1 (102.70 ± 1.56 mg/L), PLFMJ-2 (106.26 ± 1.70 mg/L), and PLFMJ-3 (107.34 ± 1.79 mg/L)) compared to the fermented juice not subject to PL (LFMJ (101.08 ± 1.43 mg/L)). These results are in line with those of Matak et al.^[47] who demonstrated that increasing exposure time of light treatment increased the concentration of volatile compounds in goat milk.

Table 4. Concentration of volatile compounds identified in pasteurized fermented mulberry beverage.

	RIL	RIExp	Compound (mg/L)	RMJ	LFMJ	TLFMJ	PLFMJ-1	PLFMJ-2	PLFMJ-3
Aldehydes
AD1	716	716	Acetaldehyde	0.20 ± 0.01	0.38 ± 0.01	0.45 ± 0.05	0.48 ± 0.02	0.53 ± 0.04	0.56 ± 0.03
AD2	1061	1060	Hexanal	0.09 ± 0.01	0.18 ± 0.02	0.12 ± 0.01	0.26 ± 0.02	0.29 ± 0.04	0.27 ± 0.05
AD3	1163	1163	Heptanal	0.53 ± 0.02	ND	ND	ND	ND	ND
AD4	1235	1232	(Z)-2-Hexenal	0.49 ± 0.01	ND	ND	ND	ND	ND
AD5	1270	1272	Octanal	0.08 ± 0.00	0.08 ± 0.00	0.06 ± 0.02	0.08 ± 0.01	0.09 ± 0.01	0.09 ± 0.02
AD6	1306	1307	(E)-2-Hepten-1-al	0.09 ± 0.01	0.05 ± 0.01	ND	ND	ND	ND
AD7	1362	1360	1-Nonanal	0.01 ± 0.01	0.02 ± 0.02	ND	0.03 ± 0.01	0.04 ± 0.03	0.04 ± 0.01
AD8	1427	1427	2-Furaldehyde	ND	ND	0.17 ± 0.01	ND	ND	ND
AD9	1497	1497	Non-2-enal	ND	ND	0.21 ± 0.02	ND	ND	ND
AD10	1556	1555	Benzaldehyde	1.07 ± 0.02	0.87 ± 0.02	ND	0.67 ± 0.04	0.54 ± 0.06	0.53 ± 0.03
AD11	1592	1591	2-Phenylethanal	0.14 ± 0.01	0.24 ± 0.01	ND	0.30 ± 0.01	0.33 ± 0.01	0.35 ± 0.02
			Subtotal	2.70 ± 0.11^a	1.82 ± 0.09^b	1.01 ± 0.11^c	1.82 ± 0.11^b	1.82 ± 0.19^b	1.84 ± 0.16^b
Acids
AC1	1404	1405	Acetic acid	2.16 ± 0.08	0.89 ± 0.02	0.77 ± 0.03	0.62 ± 0.03	0.62 ± 0.02	0.63 ± 0.02
AC2	1815	1813	Hexanoic acid	0.09 ± 0.02	ND	ND	ND	ND	ND
AC3	2016	2015	Octanoic Acid	0.48 ± 0.02	0.69 ± 0.02	0.62 ± 0.02	0.49 ± 0.02	0.43 ± 0.02	0.41 ± 0.02
AC4	2383	2381	Benzoic acid	0.19 ± 0.02	0.10 ± 0.02	0.09 ± 0.01	0.09 ± 0.01	0.08 ± 0.01	0.06 ± 0.00
			Subtotal	2.92 ± 0.14^a	1.68 ± 0.06^b	1.48 ± 0.06^b	1.20 ± 0.06^c	1.13 ± 0.05^c	1.10 ± 0.04^c
Alcohols
AL1	1064	1066	Isobutanol	0.51 ± 0.01	0.60 ± 0.01	ND	0.62 ± 0.01	0.62 ± 0.02	0.62 ± 0.02
AL2	1126	1126	1-Butyl alcohol	ND	1.12 ± 0.09	ND	1.09 ± 0.06	1.12 ± 0.05	1.12 ± 0.15
AL3	1141	1144	Pent-1-en-3-ol	ND	0.09 ± 0.01	ND	0.10 ± 0.02	0.10 ± 0.02	0.12 ± 0.04
AL4	1185	1182	3-Methyl-1-butanol	3.60 ± 0.10	3.41 ± 0.05	3.55 ± 0.12	3.38 ± 0.07	3.36 ± 0.08	3.35 ± 0.09
AL5	1251	1254	1-Pentanol	3.05 ± 0.11	3.42 ± 0.09	ND	3.38 ± 0.09	3.35 ± 0.09	3.85 ± 0.12
AL6	1316	1314	1-Hexanol	4.05 ± 0.06	4.42 ± 0.04	4.39 ± 0.09	4.42 ± 0.07	4.41 ± 0.08	4.40 ± 0.11
AL7	1370	1370	3-Ethoxypropan-1-ol	0.13 ± 0.01	0.20 ± 0.02	ND	0.19 ± 0.01	0.21 ± 0.01	0.21 ± 0.02
AL8	1434	1432	Heptyl alcohol	ND	0.12 ± 0.01	ND	0.12 ± 0.01	0.15 ± 0.01	0.21 ± 0.01
AL9	1474	1471	2-Ethylhexanol	1.58 ± 0.05	4.58 ± 0.08	1.08 ± 0.02	4.56 ± 0.06	4.61 ± 0.10	5.85 ± 0.09
AL10	1522	1523	Octan-1-ol	ND	0.06 ± 0.01	0.26 ± 0.01	0.06 ± 0.00	0.05 ± 0.00	0.05
AL11	1660	1662	Nonanol	0.66 ± 0.02	0.86 ± 0.02	0.36 ± 0.01	0.88 ± 0.02	0.87 ± 0.05	0.94 ± 0.04
AL12	1734	1732	1-Decanol	1.36 ± 0.02	ND	ND	ND	ND	ND
AL13	1863	1866	2-Phenylethyl alcohol	0.36 ± 0.02	0.42 ± 0.02	0.30 ± 0.02	0.42 ± 0.02	0.43 ± 0.04	0.49 ± 0.02
AL14	1882	1880	Benzyl Alcohol	ND	0.36 ± 0.02	ND	0.37 ± 0.02	0.38 ± 0.02	0.56 ± 0.02
			Subtotal	15.30 ± 0.40^c	19.66 ± 0.47^b	9.94 ± 0.27^d	20.99 ± 0.46^ab	22.04 ± 0.57^a	22.26 ± 0.78^a
Esters
ES1	813	813	Methyl acetate	4.41 ± 0.12	0.89 ± 0.02	0.75 ± 0.02	0.85 ± 0.02	0.82 ± 0.02	0.80 ± 0.02
ES2	828	826	Ethyl Acetate	5.89 ± 0.10	15.85 ± 0.05	5.55 ± 0.04	15.69 ± 0.09	15.63 ± 0.04	15.65 ± 0.05
ES3	985	983	Isobutyl acetate	ND	0.57 ± 0.01	0.23 ± 0.01	0.70 ± 0.07	0.78 ± 0.08	0.80 ± 0.06
ES4	1034	1035	Ethyl butyrate	0.04 ± 0.00	0.05 ± 0.00	0.04 ± 0.00	0.05 ± 0.00	0.07 ± 0.00	0.07 ± 0.00
ES5	1046	1044	Butyl acetate	ND	0.12 ± 0.01	0.12 ± 0.01	0.30 ± 0.07	0.32 ± 0.06	0.35 ± 0.07
ES6	1107	1110	Isopentyl acetate	31.72 ± 0.06	32.44 ± 0.11	31.99 ± 0.09	32.08 ± 0.11	34.48 ± 0.11	35.13 ± 0.10
ES7	1137	1140	Butyl isobutyrate	ND	0.10 ± 0.01	ND	0.25 ± 0.04	0.32 ± 0.04	0.33 ± 0.03
ES8	1161	1160	Amyl acetate	ND	0.28 ± 0.02	0.15 ± 0.00	0.30 ± 0.03	0.32 ± 0.05	0.33 ± 0.04
ES9	1171	1170	Methyl hexanoate	ND	0.58 ± 0.02	0.05 ± 0.00	0.60 ± 0.03	0.63 ± 0.04	0.65 ± 0.03
ES10	1208	1211	Ethyl hexanoate	ND	0.06 ± 0.00	ND	0.08 ± 0.00	0.10 ± 0.01	0.11 ± 0.01
ES11	1234	1234	Ethyl pyruvate	0.37 ± 0.02	0.43 ± 0.03	0.51 ± 0.04	0.48 ± 0.04	0.49 ± 0.05	0.49 ± 0.04
ES12	1251	1252	2-isopentenyl acetate	1.09 ± 0.08	ND	ND	ND	ND	ND
ES13	1256	1256	Hexyl acetate	ND	2.69 ± 0.08	2.68 ± 0.05	2.69 ± 0.06	2.45 ± 0.07	2.46 ± 0.08
ES14	1380	1378	Heptanyl acetate	ND	0.18 ± 0.01	ND	0.29 ± 0.03	0.31 ± 0.01	0.32 ± 0.08
ES15	1398	1401	Hexyl butanoate	ND	0.08 ± 0.01	ND	0.08 ± 0.01	0.09 ± 0.01	0.10 ± 0.01
ES16	1407	1407	Butyl hexanoate	ND	0.05 ± 0.01	0.05 ± 0.01	0.07 ± 0.01	0.08 ± 0.01	0.10 ± 0.02
ES17	1419	1420	Ethyl octanoate	ND	ND	ND	0.06 ± 0.01	0.07 ± 0.01	0.08 ± 0.01
ES18	1458	1458	Ethyl hexyl acetate	ND	0.13 ± 0.01	0.15 ± 0.01	0.12 ± 0.01	0.10 ± 0.01	0.10 ± 0.01
ES19	1591	1589	Methyl decanoate	ND	0.09 ± 0.01	0.06 ± 0.01	0.10 ± 0.01	0.11 ± 0.01	0.10 ± 0.01
ES20	1648	1648	Ethyl benzoate	ND	0.08 ± 0.01	ND	0.10 ± 0.01	0.11 ± 0.01	0.13 ± 0.01
ES21	1696	1694	Benzyl acetate	ND	0.20 ± 0.02	0.25 ± 0.02	0.21 ± 0.02	0.21 ± 0.01	0.20 ± 0.01
ES22	1812	1811	2-Phenylethyl acetate	9.85 ± 0.09	20.34 ± 0.12	16.44 ± 0.13	21.04 ± 0.12	21.19 ± 0.10	21.23 ± 0.15
			Subtotal	53.37 ± 0.47^d	75.21 ± 0.56^b	59.02 ± 0.44^c	76.14 ± 0.79^b	78.68 ± 0.75^a	79.53 ± 0.84^a
Furans
FS1	1221	1224	2-Pentylfuran	ND	0.03 ± 0.00	ND	0.03 ± 0.00	0.03 ± 0.00	0.03 ± 0.00
			Subtotal	0.00 ± 0.00^f	0.03 ± 0.00^d	0.00 ± 0.00^e	0.03 ± 0.00^c	0.03 ± 0.00^b	0.03 ± 0.00^a
Phenols
VP1	1873	1874	2-Methoxylphenol	0.01 ± 0.0	0.02 ± 0.00	0.02 ± 0.00	0.03 ± 0.00	0.03 ± 0.00	0.03 ± 0.00
VP2	2088	2090	Methoxy-4-allylphenol	ND	0.16 ± 0.02	0.10 ± 0.01	0.11 ± 0.01	0.11 ± 0.02	0.12 ± 0.03
VP3	2381	2382	2,4-Di-tert-butylphenol	ND	2.15 ± 0.20	1.25 ± 0.12	2.13 ± 0.10	2.14 ± 0.09	2.15 ± 0.10
VP4	2393	2396	4-vinylphenol	0.01 ± 0.0	ND	ND	ND	ND	ND
			Subtotal	0.02 ± 0.00^c	2.33 ± 0.22^a	1.37 ± 0.13^b	2.27 ± 0.11^a	2.28 ± 0.11^a	2.30 ± 0.13^a
Lactones
LS1	1998	1996	γ- Nonanolactone	ND	ND	0.02 ± 0.0	ND	ND	ND
LS2	1201	1203	D-Limonene	ND	0.02 ± 0.00	ND	0.02 ± 0.00	0.03 ± 0.00	0.03 ± 0.00
			Subtotal	0.00 ± 0.00^f	0.02 ± 0.00^e	0.02 ± 0.00^d	0.02 ± 0.00^c	0.03 ± 0.00^b	0.03 ± 0.00^a
Ketone
KE1	984	984	3-Pentanone	ND	0.03 ± 0.00	ND	ND	ND	ND
KE2	1060	1059	Hexen-3-one	ND	0.01 ± 0.00	0.03 ± 0.00	ND	ND	ND
KE3	1166	1165	2-Heptanone	ND	0.07 ± 0.01	0.05 ± 0.01	0.07 ± 0.01	0.06 ± 0.00	0.07 ± 0.00
KE4	1242	1240	3-Octanone	0.03 ± 0.00	ND	ND	ND	ND	ND
KE5	1309	1311	4-Octen-3-one	ND	0.13 ± 0.01	0.18 ± 0.02	0.15 ± 0.02	0.18 ± 0.03	0.17 ± 0.02
KE6	1311	1313	Methyl heptenone	0.02 ± 0.0	0.01 ± 0.00	ND	ND	ND	ND
KE7	1374	1374	Nonan-2-one	ND	0.07 ± 0.01	ND	ND	ND	ND
KE8	1788	1793	(E)-β-Damascenone	0.01 ± 0.00	0.01 ± 0.00	ND	0.01 ± 0.00	0.01 ± 0.00	0.01 ± 0.00
			Subtotal	0.06 ± 0.00^c	0.33 ± 0.03^a	0.26 ± 0.03^b	0.23 ± 0.03^b	0.25 ± 0.03^b	0.25 ± 0.02^b
			Total	74.37 ± 1.12^d	101.08 ± 1.43^c	73.10 ± 1.04^d	102.70 ± 1.56^bc	106.26 ± 1.70^ab	107.34 ± 1.79^a

Data expressed as mean ± standard deviation

Means that do not share a letter are significantly different (P < 0.05).

RMJ: raw mulberry juice; LFMJ: lactic-acid-fermented mulberry juice; TLFMJ: thermal pasteurized fermented mulberry juice; PLFMJ: pulsed light pasteurized fermented mulberry juice (exposure time of 1 – 2 s; 2 – 4 s; 3 – 4 s)

ND: Not detected

Experimental retention index (RIExp) on a DB-Wax column (Agilent Technologies, Santa Clara, California, USA). Retention index from the literature (RIL).^[31]

Odor activity values assessment

The core aromatic notes of the samples as illustrated by their odor activity value (OAV) are presented in Table 5. The PL treatments had positive impact on the OAV of the fermented sample with the highest OAV of 541.56 after exposure time of 8 s. The TLFMJ on the other hand recorded the least OAV of 259.08 (Table 5). This could be due to the effect of heat on the key odorants responsible for the aroma of the juice.^[48] A total of 32 (48.48%) aromatic compounds out of the 66 volatile compounds identified (Table 4) were noted to be accountable for the aromatic notes of the juice (Table 5). Based on the classifications of odorants compounds (odorant with OAV > 1 are significant and those <1 but > 0.2 may have synergistic impact on product’s aroma),^[49,50] odorants that had significant impact (OAV > 1) on the aromatic tone of the PL treated samples were 2-phenylethyl acetate, (E)-β-damascenone, acetaldehyde, 1-nonanal, 3-ethoxypropan-1-ol, heptyl alcohol, ethyl acetate, isopentyl acetate, ethyl hexanoate, octanal, and hexyl acetate. In addition, ethyl butyrate, benzaldehyde, 2-phenylethanal, isobutyl acetate, butyl acetate, 1-hexanol, ethyl octanoate, and ethyl benzoate were found to have possible synergistic impact on the aromatic tone of the juice (Table 5).

Table 5. Effect of pulsed light treatments on odor activity values of potent odorant compounds in lactic-acid-fermented mulberry juice.

	RMJ	LFMJ	TLFMJ	PLFMJ-1	PLFMJ-2	PLFMJ-3	Aroma series	OT (g/L)
Aldehydes
AD1	1.67	3.17	3.75	4.00	4.42	4.67	Fruity, floral,	0.12
AD4	1.40	0.00	0.00	0.00	0.00	0.00	Floral, chemical, fruity	0.35
AD5	53.33	53.33	40.00	53.33	60.00	60.00	Fruity, chemical	0.0015
AD7	7.69	15.38	0.00	23.08	30.77	30.77	Fruity	0.0013
AD10	0.54	0.44	0.00	0.34	0.27	0.27	Fruity, chemical	2
AD11	0.14	0.24	0.00	0.30	0.33	0.35	Fruity	1
Subtotal	64.77	72.56	43.75	81.05	95.79	96.05
Acids
AC2	0.03	0.00	0.00	0.00	0.00	0.00	Fruity, nutty	3
AC3	0.05	0.07	0.06	0.05	0.04	0.04	Nutty	10
Subtotal	0.08	0.07	0.06	0.05	0.04	0.04
Alcohols
AL1	0.01	0.01	0.00	0.01	0.01	0.01	Chemical	75
AL2	0.00	0.01	0.00	0.01	0.01	0.01	Chemical	150
AL4	0.12	0.11	0.12	0.11	0.11	0.11	Chemical	30
AL5	0.05	0.05	0.00	0.05	0.05	0.06	Fruity	64
AL6	0.51	0.55	0.55	0.55	0.55	0.55	Fruity, floral	8
AL7	1.30	2.00	0.00	1.90	2.10	2.10	Fruity	0.1
AL8	0.00	1.20	0.00	1.20	1.50	2.10	Fruity	0.1
AL10	0.00	0.07	0.29	0.07	0.06	0.06	Nutty	0.9
AL12	3.40	0.00	0.00	0.00	0.00	0.00	Balsamic	0.4
AL13	0.04	0.04	0.03	0.04	0.04	0.05	Fruity, chemical, floral	10
Subtotal	5.42	4.04	0.99	3.94	4.43	5.04
Esters
ES2	0.49	1.32	0.46	1.31	1.30	1.30	Fruity, microbiological	12
ES3	0.00	0.36	0.14	0.44	0.49	0.50	Fruity	1.6
ES4	0.20	0.25	0.20	0.25	0.35	0.35	Fruity	0.2
ES5	0.00	0.30	0.30	0.75	0.80	0.88	Fruity	0.4
ES6	198.25	202.75	199.94	200.50	215.50	219.56	Fruity	0.16
ES10	0.00	0.75	0.00	1.00	1.25	1.38	Fruity, floral	0.08
ES11	0.07	0.09	0.10	0.10	0.10	0.10	Caramel, fruity	5
ES13	0.00	4.01	4.00	4.01	3.66	3.67	Fruity, floral	0.67
ES17	0.00	0.00	0.00	0.25	0.29	0.33	Fruit, floral	0.24
ES20	0.00	0.16	0.00	0.20	0.22	0.26	Fruity, Floral, Chemical	0.5
ES22	5.47	11.30	9.13	11.69	11.77	11.79	Floral	1.8
Subtotal	204.49	221.29	214.28	220.49	235.73	240.12
Phenols
VP4	0.06	0.00	0.00	0.00	0.00	0.00	Phenolic, roasty	0.18
Subtotal	0.06	0.00	0.00	0.00	0.00	0.00
Lactones
LS1	0.00	0.00	0.80	0.00	0.00	0.00	Fruity	0.025
Subtotal	0.00	0.00	0.80	0.00	0.00	0.00
Ketone
KE8	200.00	200.00	0.00	200.00	200.00	200.00	Fruity, floral	0.00005
Subtotal	200.00	200.00	0.00	200.00	200.00	200.00
Total	474.80	497.96	259.08	505.53	535.99	541.26

RMJ: raw mulberry juice; LFMJ: lactic-acid-fermented mulberry juice; TLFMJ: thermal pasteurized fermented mulberry juice; PLFMJ: pulsed light pasteurized fermented mulberry juice (exposure time of 1 – 2 s; 2 – 4 s; 3 – 4 s)

Volatile compounds were coded as indicated in Table 4

Odor threshold were obtained from the literature^[50,52]

Aromatic series were from the literature^[53,54]

Principal component analysis

PCA was performed using the identified volatiles (Table 4) to highlight the effect of the PL treatment on the LFMJ volatile profile. A 98.28% of the total variance could be explained by the first three principal components (PC1 (62.33%), PC2 (27.88%), and PC3 (8.07%)) with highest eigenvalue (Fig. 1). The PL treated samples (PLFMJ-1, PLFMJ-2, and PLFMJ-3) that were closely related were located on the positive side of PC3 and negative sides of PC1 and PC2. These samples were mostly associated with AD2, AD5, AD11, AC3, AL8, AL13, ES3, ES4, ES6, ES7, ES10, ES14, ES17, ES20, LS2, and KE2. The sample located on the negative side of PC2 and positive sides of PC1 and PC3 was RMJ. The RMJ was characterized by AD3, AD4, AC2, AL6, AL12, ES1, ES12, VP4, and KE4. The TLFMJ, which was categorized by AD8, AD9, AL4, AL10, and LS1, was situated on the positive sides of PC1, PC2, and PC3. The LFMJ was situated on the negative sides of PC1, PC2, and PC3. It was characterized by AL1, AL2, AL3, AL5, AL7, AL9, AL11, AL14, ES2, ES9, ES15, FS1, KE2, KE7, and KE8. With regard to the factor scores of the first three principal components (Table 6), the samples were divided into four groups according to the link between the treatments (scores) and their volatile properties (loadings) as shown in Fig. 1b.

Table 6. Factor scores of the first three principal components.

	PC1	PC2	PC3
RMJ	10.604	−4.984	0.657
LFMJ	−1.410	−0.308	−4.590
TLFMJ	4.807	7.999	0.699
PLFMJ-1	−3.426	−0.310	0.202
PLFMJ-2	−4.782	−0.967	1.432
PLFMJ-3	−5.792	−1.430	1.600

RMJ: raw mulberry juice; LFMJ: lactic-acid-fermented mulberry juice; TLFMJ: thermal pasteurized fermented mulberry juice; PLFMJ: pulsed light pasteurized fermented mulberry juice (exposure time of 1 – 2 s; 2 – 4 s; 3 – 4 s)

PC – principal component

Figure 1. Principal component analysis of the volatile profile of pulsed light treated lactic-acid-fermented mulberry juice: (A) loading plot; (b) scores scatter plot. RMJ – raw mulberry juice, LFMJ – lactic-acid-fermented mulberry juice, TLFMJ – thermal pasteurized fermented mulberry juice, PLFMJ – pulsed light pasteurized fermented mulberry juice (exposure time of 1 – 2 s; 2 – 4 s; 3 – 4 s). Coded volatiles are as shown in Table 4.

Sensory assessment

The mean sensory scores of the juices are presented in Fig. 2. The fermented samples were scored higher in all the assessable areas compared to the unfermented juice.^[51] Among the fermented samples, the Pl treated samples had higher mean scores in terms of color, aroma, taste, flavor, and mouthfeel whereas the thermal treated sample had lower scores. These confirm the detrimental effect of thermal treatment on the juice color (Table 2) and the OAV (Table 5) and the positive influence of PL on the volatile and phytochemicals characteristics of the juice as discussed earlier. The flavor of the PL treated juices as perceived by the panelist followed a similar trend as the OAV of the juices (Table 5). The overall acceptability scores depict that PLFMJ-2 was the most preferred (Fig. 2).

Figure 2. Sensory assessment of thermal and pulsed light thermal treated lactic-acid-fermented mulberry juice. RMJ – raw mulberry juice, LFMJ – lactic-acid-fermented mulberry juice, TLFMJ – thermal pasteurized fermented mulberry juice, PLFMJ – pulsed light pasteurized fermented mulberry juice (exposure time of 1 – 2 s; 2 – 4 s; 3 – 4 s). Values in the same grouped column with different superscript letters are significantly different at P < 0.05.

Conclusion

This study demonstrated that pulsed light is effective in reducing microbial levels in fermented mulberry juice without changing their physicochemical properties. Pulsed light also enhances the total phenolics, volatile composition, and the aromatic tones of lactic-acid-fermented mulberry juice with increasing pulsation time. The results also suggested that total anthocyanin concentration of lactic-acid-fermented mulberry juice is unlikely to be damaged under short PL exposure time. The sensory analysis revealed that the nonthermal treated fermented juices were more preferred than the pasteurized fermented juice. This clearly shows that the integration of PL into juice processing lines could be considered a modest and cost-effective substitute to improve the safety and quality of juices.

Conflict of interest statement

The authors declare no conflict of interest.