Effect of Storage on 5-Hydroxymethylfurfural (HMF) Formation and Color Change in Jams

Abstract

In this study, the effects of storage temperature (10, 20, and 37°C) and time (0, 2, 4, and 6 months) on the HMF and color values in strawberry, cherry and apricot jams were studied. Results showed that the HMF and total color difference (ΔE) values of all jams were increased linearly with storage time and higher values were found at higher storage temperature. Kinetic model was applied to changes in HMF and ΔE. Changes in HMF and ΔE were explained using zero-order reaction kinetics and the dependence of the rate constant on temperature was described by the Arrhenius equation

Keywords:

• Jams
• Storage
• 5-Hydroxymethylfurfural
• Color
• Kinetics

INTRODUCTION

Maillard reaction can occur during the manufacture and storage of heat-processed foods that contain sugar and amino acids and it is associated with change of color and flavors,[1,2] decrease in the nutritional value of foods[3,4] and increase in health hazards.[5] HMF is an important intermediate product of the Maillard reactions and is used as an indicator of the severity of heat treatment in manufacturing and unsuitable storage conditions of various foods, such as jams,[6,7] fruit juices and concentrates,[4,8,9] infant foods,[7] dried fruit,[10] and honey.[11–13] Therefore, the Codex Alimentarius of the World Health Organisation, Council of the European Union and other many countries have established a maximum HMF level in different foods

HMF is an important component for jams because of their high carbohydrate content. HMF content of jams can be increased with storage at unsuitable conditions during marketing. Mendoza et al.[7] declared that HMF value increased from 0.6 to 35.2 mg/100 g in stored commercial peach jams after 12 month at 35°C. Same result was observed in apricot jam by Trifiro and Landi.[14] They found that HMF content of apricot jam increased from 0.25 mg/100 g to 29.8 mg/100 g after 2 months storage at 45°C. Babsky et al.[4] declared that in an apple juice concentrate, properly produced and stored, the HMF content was considerably lower than 10 mg/100 g, but it was more than 40 mg/100 g after 100 days at 37°C

Some studies related to the HMF contents and color values of jams were reported by different authors.[6,7,15,16] However, studies related with color changes together with HMF formation during storage in jams are limited. This study aims at investigating the relationship of color change with HMF formation in strawberry, cherry and apricot jams at different storage temperatures and times

MATERIALS AND METHODS

Materials

Strawberry, cherry and apricot jams were obtained from Yenigün Co. (Antalya, Turkey). Jams were stored in glass jars (720 cc) in the dark at 10, 20, and 37°C during 6 month. Samples were taken in duplicate at 0, 2, 4, and 6 months of storage, and HMF, °brix, pH and hunter Lab (L, a, b) were measured in samples. Prior to analytical measurement, all samples were homogenized using an Ultra-Turrax homogenizer (IKA-WERKE, Germany)

Methods

Soluble solids and color measurement

Soluble solid were measured as °brix using an abbe refractometer (Atago Rx 5000α). Hunter Lab values (L, a, b) of jams were determined with a Konica Minolta chromameter (CR-400). The color of a sample is denoted by the three dimensions L, a, and b values. The L value gives a measure of the lightness of the product color from 100 for perfect white to zero for black, as the eye would evaluate it. The a value indicates a measure of redness when positive, grey when zero, and greenness when negative, and b measures yellowness when positive, grey when zero, and blueness when negative. Color measurements were carried out in triplicate

During storage, the color changes of jams can also be expressed as a single numerical value ΔE. This value defines the magnitude of the total color difference. The ΔE value is expressed by the following equation:

(1)

where L₀, a₀, and b₀are represented the reading at time zero, and L, a, and b are represented the instantaneous individual readings during storage

Chemical analyses

Titratable acidity and pH were estimated according to AOAC.[17] Total sugar and invert sugar were quantified according to the Lane-Eynon method.[18]

Determination of HMF

One gram sample was accurately weighed into a 10 ml volumetric flask and diluted to volume with water. The dilution was centrifuged at 15893 × g for 10 min. Supernatant was filtered through a 0.45 μm filter before injection. Chromatographic analyses were carried out on an HPLC system (Shimadzu, Kyoto, Japan) that consisted of a LC-10 AD-VP gradient pump, a Rheodyne 7725i valve furnished with 20 μl loop, a SPD-M10A photodiode array detector, CTO-10AS column oven, DGU-14A degasser, and a SCL-10A system controller

Some modifications of method described earlier by Gokmen et al.[19] and Wang et al.[20] were used for HPLC. Separation of HMF was carried out using an ACE 5 C18 (250 × 4.6mm id, particle size 5 μm) column (Scotland). The elution was done in the isocratic mode with a mixture of acetonitril (10%) and water (90%) using a flow rate of 1 mL/minute at 40°C. Detection was made at 276 nm. The HMF was identified on retention times and spectral data by comparison with commercial standards (Sigma, H9877, St Louis, MO, USA)

Statistical Analysis

Data were analyzed using the SAS/STAT (SAS. Ins. Inc. Cri. NCI) software for one-way ANOVA and correlation coefficients

RESULTS AND DISCUSSION

The °brix, pH, titratable acidity, total sugar and invert sugar in the beginning samples are given in Table 1. As seen in Table 1, while the °brix, total sugar and reducing sugar values of Cherry jams were higher than strawberry and apricot jams, pH values of them were very similar. The changes in °brix, pH and HMF values of jams during storage at 10, 20, and 37°C for 6 months are shown in Table 2. In jam products, results showed no significant changes in the °brix and pH values at all temperatures.

Table 1 Chemical compositions of beginning jam samples

Chemical composition	Strawberry jam	Cherry jam	Apricot jam
°Brix	72.70	80.63	70.55
Titratable acidity (% w/v, as citric acid)	0.218	0.504	0.441
pH	3.62	3.48	3.40
Total sugar (%)	47.46	53.82	45.43
Invert sugar (%)	44.52	52.05	41.81

Table 2 Effect of storage time and temperature on °brix, pH and HMF (mg/kg)

		Strawberry jam			Cherry jam			Apricot jam
T (°C )	Time (month)	°Brix	pH	HMF	°Brix	pH	HMF	°Brix	pH	HMF
10	0	72.70	3.62	20.39	80.63	3.48	34.18	70.55	3.40	30.83
	2	72.74	3.58	21.24	78.03	3.49	34.48	70.62	3.39	30.99
	4	73.17	3.60	22.39	80.42	3.46	34.88	70.65	3.43	31.17
	6	72.58	3.61	23.03	79.20	3.44	35.45	69.79	3.38	31.68
20	0	72.70	3.62	20.39	80.63	3.48	34.18	70.55	3.40	30.83
	2	72.93	3.63	23.42	79.35	3.40	37.02	71.05	3.38	31.92
	4	73.82	3.64	26.64	80.50	3.44	39.21	70.09	3.39	32.53
	6	73.70	3.57	28.19	79.58	3.50	41.02	69.64	3.40	34.25
37	0	72.70	3.62	20.39	80.63	3.48	34.18	70.55	3.40	30.83
	2	73.05	3.62	48.06	79.61	3.52	89.63	70.39	3.40	82.51
	4	72.32	3.53	107.00	79.80	3.51	244.00	69.39	3.42	210.70
	6	73.08	3.60	161.50	79.96	3.46	422.70	70.39	3.41	319.20

The initial values of HMF in strawberry, cherry, and apricot jams were 20.39, 34.18 and 30.83 mg/kg, respectively. Low HMF formation was observed during storage at 10 and 20°C in all jams studied. The amounts of HMF between 10 and 20°C were not shown a significant difference in all jam samples (P > 0.05). However, a great increase in HMF was observed during storage at 37°C. HMF reached its maximum values after 6 month at 37°C in all jams. HMF content of strawberry, cherry and apricot jams increased from 20.39 to 161.5 mg/kg, 34.18 to 422.7 mg/kg, and 30.83 to 319.2 mg/kg, respectively. Our finding results were higher than the findings of Mendoza et al.[7] and Trifiro and Landi[14]. While initial HMF values in all jams were acceptable, HMF values were higher than acceptable values at the end of the storage at 37°C. The formation of HMF during storage at 37°C in cherry jams was higher than strawberry and apricot jams. This situation may be due to the high °brix and sugar content of cherry jams. Şimsek et al.[8] identified that when °brix degrees were altered from 15° to 65°, HMF contents increased in white and red grape juice

Kinetic rate constant together with the activation energy (Ea) values for HMF contents of jams are reported in Table 3. The coefficients of determination (R²) were accounted from each relation for zero- and first-order reactions for all parameters studied in all jam samples.

Table 3 Kinetic rate constant, Ea, and correlation coefficients accounted for HMF formation in jams stored at various temperatures

Jams	T (°C)	k0 (month^−1)	R^2	Ea (kJ mol^−1)	R^2
Strawberry				109.17	0.982
	10	0.45	0.984
	20	1.33	0.892
	37	24.11	0.984
Cherry				157.43	0.988
	10	0.21	0.999
	20	1.14	0.911
	37	66.0	0.977
Apricot				162.83	0.970
	10	0.14	0.994
	20	0.54	0.992
	37	49.66	0.979

(2)

(3)

where C and C₀are the final and initial concentration, k₀and k₁are the reaction rate constants, and t is the duration of storage (month).The temperature dependence of a reaction rate constant is described by the Arrhenius equation:

(4)

where k is the reaction rate constant, A is the frequency factor, Ea is the activation energy, R is the gas constant (8.314 J mol⁻¹K⁻¹), and T is the absolute temperature (K)

The results indicated that HMF increased linearly with time and higher amounts were found at higher temperature during storage. In general, determination coefficients (R²) were higher in the zero-order rate than in the first-order. Therefore, zero order kinetics was applied to describe the change of HMF content. Rate constant values tended to increase with storage temperature. This situation indicates a higher HMF formation at high temperature. When rate constant values in jams were compared, cherry jams showed higher rate constant than apricot and strawberry. The activation energy obtained was 109.17 kJ mol⁻¹for strawberry jams, and 157.43 kJ mol⁻¹for cherry jams, and 162.83 kJ mol⁻¹for apricot jams. These results showed that apricot and cherry jams are much more sensitive to storage temperature than strawberry jams for HMF formation

The light conditions (10 and 20°C) during 6 month storage did not affect the color values of the strawberry, cherry and apricot jams, but the storage at 37°C greatly affected the color values of all jams (Table 4). While L values (100 white, 0 black) of strawberry and apricot jams were decreased during storage, interestingly, L value of cherry jams was increased. While a values of strawberry and cherry were decreased with storage at all temperature, a values of apricot jams was increased and b values of all samples were decreased. A decrease in L values and an increase in a values in apricot jams during storage may be indicated the formation of characteristic brown pigment of Maillard reactions. Similar results were declared for white hard grape pekmez by Tosun and Ustun.[1] Decreases in values of strawberry and cherry jams could be associated with degradation of anthocyanins. Wicklund et al.[21] declared that a high positive correlation between the a value and anthocyanin content in strawberry cultivars was detected (r= 0.95). Anthocyanins are natural pigments of strawberry and cherry, and are unstable with degradation of the pigments during processing and storage of food tissues.[22] The anthocyanin structure is transformed through ring opening to the pale yellow or colorless chalcone form.[23]

Table 4 Effect of storage time and temperature on hunter color values (L, a, b) and ΔE

		Strawberry jam				Cherry jam				Apricot jam
T (°C)	Time (month)	L	a	b	ΔE	L	a	b	ΔE	L	a	b	ΔE
10	0	28.17	12.81	7.32	0.00	22.09	13.45	4.05	0.00	41.50	3.64	18.70	0.00
	2	27.59	13.15	7.52	0.71	22.42	13.33	4.05	0.42	40.53	3.86	17.50	1.55
	4	27.76	11.66	7.36	1.22	22.53	13.01	4.03	0.63	40.97	3.91	16.90	1.90
	6	27.74	11.38	7.30	1.49	22.64	13.96	4.01	0.75	40.38	4.06	18.10	1.36
20	0	28.17	12.81	7.32	0.00	22.09	13.45	4.05	0.00	41.50	3.64	18.70	0.00
	2	27.69	12.47	7.21	0.60	23.49	13.56	4.02	1.42	40.19	4.26	18.00	1.57
	4	27.30	11.93	7.23	1.24	23.51	13.32	4.09	1.43	38.86	4.43	17.60	3.39
	6	26.98	11.14	7.14	2.05	23.54	13.68	4.00	1.47	38.27	4.52	16.00	4.24
37	0	28.17	12.81	7.32	0.00	22.09	13.45	4.05	0.00	41.50	3.64	18.70	0.00
	2	27.83	7.54	7.19	5.28	23.27	9.54	3.99	4.09	39.23	4.64	17.20	2.91
	4	26.36	6.69	7.12	6.38	24.33	9.69	3.88	4.38	38.18	5.07	14.60	5.47
	6	26.04	6.86	6.99	6.32	25.02	9.90	3.56	4.63	36.14	5.04	13.30	7.74

ΔE is a informative colorimetric parameter extensively used to characterize the color changes in foods during processing and storage,[24,25,26] and is a combination of parameters L, a, and b. ΔE was increased with storage time and temperature. Although high ΔE values were found in the jams stored at 37°C, the largest color change during storage at all temperature was observed in apricot jams. Color changes of foods may be the result of more than one reaction, and are influenced by both non-enzymatic browning and pigment destruction. The first stage is color formation due to the Maillard reaction, which followed a zero-order kinetics (k₀). The second stage is the destruction of natural fruit pigments, which follow first-order kinetics (k₁). Thus, different researchers suggested using combined model to explain the effect of thermal processing on ΔE [27,28]:

(5)

where Kc = k₀/k₁

In this study, the results showed that determination coefficients were higher in zero-order kinetic than in the first-order kinetic and combined kinetic model. Thus, ΔE values were processed according to zero-order kinetics, and rate constant values and corresponding Ea values are reported in Table 5. ΔE values obtained during storage of processed tomato products also were processed according to zero-order kinetics by Giovanelli and Lavelli.[29] This indicated that Maillard reaction predominated over pigment destruction during storage in this study conditions.

Table 5 Kinetic rate constant, Ea and correlation coefficients accounted for ΔE values in jams stored at various temperatures

Jams	T (°C)	k0(month^−1)	R^2	Ea (kJ mol^−1)	R^2
Strawberry				38.66	0.963
	10	0.25	0.935
	20	0.34	0.993
	37	1.00	0.727
Cherry				47.53	0.990
	10	0.12	0.907
	20	0.22	0.632
	37	0.71	0.693
Apricot				46.37	0.904
	10	0.22	0.464
	20	0.71	0.997
	37	1.29	0.997

ΔE values increased almost linearly with time in all samples. The highest ΔE values were found at higher temperature conditions during storage. Rate constant values tended to increase with storage temperature. Apricot jams values had higher rate constants than strawberry and cherry jams. The high rate constant values indicate a higher color change. Consequently, apricot jams showed higher color change than the strawberry and cherry jams. The activation energy accounted for ΔE is 47.53 kJ mol⁻¹for cherry, and 46.37 kJ mol⁻¹for apricot, and 38.66 kJ mol⁻¹for strawberry. Cherry and apricot jams are much more sensitive to storage temperature than strawberry jams

When HMF and color values were compared, significant correlations (P < 0.01) were found between the HMF and L, the HMF and a, the HMF and b, the HMF and ΔE in all jams (Table 6). Highest correlation values in strawberry and cherry jams were found between the HMF and b and the HMF and ΔE. On the other hand, the highest correlation values were found between the HMF and L and the HMF and ΔE in apricot jam. A high correlation between HMF and ΔE was found in all jams. According to these results, HMF could be use as a parameter to evaluate the color change.

Table 6 Correlation coefficients between the HMF and color values (L, a, b, and ΔE) of jams (P < 0.01)

	HMF (mg kg^−1)
Color values	Strawberry jam	Cherry jam	Apricot jam
L	−0.811	0.832	−0.868
a	0.778	−0.759	−0.843
b	−0.903	−0.948	−0.720
ΔE	0.879	0.811	0.860

CONCLUSIONS

Results showed that °Brix and pH values during the storage of strawberry, apricot, and cherry jams at 10, 20, and 37°C for 6 months were not significantly changed. It was found that a large dependence of the formation of HMF on time and temperature of storage. HMF increased linearly with time and higher amounts were found at higher temperature. A great increase in HMF during storage at 37°C in all jams was observed and HMF reached its maximum values at the end of the storage in all jams. It was also found that significant changes in color values (L, a, b, and ΔE) with time and temperature of storage. Significant correlations were found between HMF and color values. When activation energies obtained for HMF and ΔE were compared, the activation energy found for HMF formation was higher than that of ΔE. This implied that HMF formation occurred at a higher rate than color change. HMF retained in the jams would change to a brown pigment during storage. Therefore, HMF could be use as a parameter to evaluate the color change and non-enzymatic browning during storage