Curing properties of sodium nitrite in restructured goat meat (chevon) jerky

ABSTRACT

Known curing impacts on goat meat (chevon) is limited due to the low production and consumption of chevon products in the United States. This study, therefore, assessed sodium nitrite influences on the quality parameters of restructured chevon jerky and its stability. Inclusion of NaNO₂ increased (p < 0.01) the redness of chevon jerky (14.2 versus 8.17); however, the redness was decreased (p < 0.01) over a 30 d storage period. The texture properties and microbial counts of jerky were not influenced by NaNO₂. However, the total microbial counts increased (1.84 to 6.00 ± 0.468 log CFU/g; p < 0.01) with storage time in chevon jerky whether or not nitrite was included. Inclusion of NaNO₂ decreased (p < 0.05) thiobarbituric acid reactive substances values (4.26 versus 4.81 mg MDA/kg), which did not change during storage. Among 28 isolated fatty acids from chevon jerky, palmitic (C16:0), stearic (C18:0), oleic (C18:1n9), and linoleic (C18:2n6) acids were the major four fatty acids. Of the 21 positively identified volatile compounds, six terpenes (α-pinene, β-pinene, β-phellandrene, carene, limonene, and cubebene), octanone and nonanal were the most abundant compounds. Neither processing treatment nor storage time significantly influenced the concentration of individual fatty acids and volatile compounds. Cured jerky had higher (p < 0.05) sensory color and flavor scores compared to uncured jerky. Results indicated that inclusion of NaNO₂ might improve color and sensory properties, as well as control the lipid oxidation of chevon jerky. However, the reduction of lipid oxidation in jerky was not revealed in product fatty acid or volatile flavor compounds.

KEYWORDS:

• Restructured jerky
• Goat meat
• Chevon
• Sodium nitrite
• Flavor

Introduction

Jerky is a dried meat product that is traditionally preserved by salting and drying. Numerous jerky products have been made from a variety of different meats (beef, pork, poultry, venison, and fish) with different marinating and processing techniques.^[1] Previously, jerky processors had only relied upon achieving a final moisture-to-protein ratio (MPR) of ≤0.75:1 to meet the standard of identity for jerky that is not a safety parameter. Consequently, it has been suggested that jerky products should be dried to a water activity (a_w) level of ≤0.85 to ensure safety and control pathogens.^[2]

Jerky made from beef has been more widely consumed than that from other meats in the United States. However, the demand of jerky made from other meats has steadily increased. Goat meat (chevon) is characterized by possessing a low intramuscular fat level which is characterized by possessing an increased unsaturated/saturated fats ratio and low cholesterol content.^[3] Compared with beef jerky, the production of chevon jerky is a rather empirical process and final products suffer from quality problems during processing and storage. According to Eega et al.,^[4] sliced whole muscle chevon jerky had inferior organoleptic and sensory properties compared to beef jerky. Comminuted jerky-type products have softer texture properties compared to sliced whole muscle jerky.^[5] Restructured jerky can be made from minced and/or chopped muscles and produce products with a more consistent appearance and texture.^[1] Compared with sliced whole muscle jerky, comminuted jerky has higher a_w and fat contents, resulting in a product that is more susceptive to microbial growth and lipid oxidation.^[5]

Sodium nitrite (NaNO₂) is considered an essential ingredient of curing meat, which is responsible for fixing the characteristic red color and creating a unique flavor in the cured meat, as well as preventing lipid oxidation and microbial growth.^[6] The use of sodium nitrite for curing, however, has generated extensive debate because of its potential to generate carcinogenic nitrosamines via the interaction of amines with nitrites (NO₂⁻) at higher temperatures.^[7] The beneficial effects of nitrites are overwhelming against the negligible chance to form nitrosamines (>130ºC) during the curing processing. Meat products, in general, noticeable differences exist between the cured and uncured versions of the same product. Yet it is still not clearly known what is responsible for these differences. Furthermore, the knowledge of curing effects such as color and flavor, as well as retarding of lipid oxidation and microbial growth on chevon is limited due to the low product and consumption of chevon in the United States. The purpose of this study was to product shelf-stable restructured chevon jerky and to determine the extent of sodium nitrite impacts on quality parameters of produced jerky and its stability during storage.

Materials and methods

Preparation of restructured chevon jerky with or without sodium nitrite (NaNO₂)

Spanish purebred intact male goats (9-month-old), graze on ray grass and clover dominated forages, were slaughtered and chilled at 2°C for 24 h at Fort Valley State University (Fort Valley, GA, USA). Carcasses were fabricated on day 2 postmortem and the legs and shoulders as well as accompanying trim were collected and vacuum-packaged (Cryovac Inc., Duncan, SC, USA) and stored at –18°C until processed. Partial thawed, frozen chevon at 2°C was ground through a 9.5 mm grinder plate (a coarse grinding) and then re-ground through a 3.2 mm grinder plate (a fine grinding) using a commercial meat grinder (BIRO Model 7552 SS4; BIRO Manufacturing Co., Marblehead, OH, USA). The ground chevon (9.07 kg) was placed in a Fleetwood meat mixer (Model MMS-50I; Skymsen Equipment LLC, Newark, NJ, USA). The chevon was mixed with jerky seasoning (273 g) consisted of salt, sugar, hydrolyzed soya protein (15.38%), spices, sodium erythorbate, spice extractive, and less than 2% silicon dioxide added to prevent caking, plus either with or without sodium nitrite (NaNO₂; 0.015%, w/w). The mixture (9.34 kg/batch) was stored under refrigeration overnight and then extruded through a flat jerky nozzle (3.00 × 0.48 cm) using a jerky extruder (Jerky Cannon; L.E.M. Products, Inc., Harrison, OH, USA) on trays (82.7 × 62.5 × 2.3 cm). The trays were placed in a pre-heated oven (Model 100XLT-1, Kemette, Corp., Charlotte, NC, USA) and held at 93.3°C for 3.5 h. The processed jerky was then removed from the oven and air-dried for 1 h under forced airflow at ambient temperature, and cut into 10.0 cm long strips.

Two batches of chevon jerky with and without sodium nitrite (NaNO₂) were produced within a same day for 4 days in 2 consecutive weeks by using the same procedures described previously. Four replications were generated and a single replication consisted of jerky made from the same day. In each individual batch, jerky strips (10.0 × 2.0 × 0.3 cm) were randomly selected, vacuum-packaged (Model UV2100-C Ultravac Koch; Koch Equipment Ultrasource, Kansas City, MO, USA) in vacuum pouches (six strips/pouch; 30 to 50 mL of O₂/m²/24 h/1 atm at 25°C; Cryovac Inc., Duncan, SC, USA), and stored for 30 d at ambient temperature under fluorescent light (150–200 lux). Physicochemical, microbial, and sensory properties of chevon jerky prepared either with or without sodium nitrite, were determined at 1, 15, and 30 d of storage.

Physicochemical properties

The physical properties of color and shear forces were measured on restructured chevon jerky during 30 d of storage. Among the chemical properties assessed, proximate compositions, and MRPs were determined with only fresh (1 d) jerky samples. However, other chemical properties, such as; water activity (a_w), pH, 2-thiobarbituric acid reactive substances (TBARS), fatty acid composition, and volatile compounds were analyzed over the 30 d of ambient storage.

Color measurements

The CIE L* a* b* color coordinate values were measured from the surface of jerky samples from each batch over the 30 d storage using HunterLab color units (Minolta Chromameter, Model CR-200, Minolta, Japan) with illuminant D65 as a light source. Hue angle and chroma values were calculated according to Hunter and Harold.^[8] After 1, 15, and 30 d of storage, jerky strips from individual batches were removed from vacuum pouches, and randomly selected six strips. Measurements were taken at three different areas (top, middle, and bottom) from each selected strip.

Texture measurements

Shear values of the jerky strips were measured using a TA-XT2 texture analyzer equipped with a Warner-Bratzler shear attachment (Texture Technologies Corp., Scarsdale, NY, USA) as described by Lee et al.^[9] Prepared individual jerky samples (2.0 × 2.0 × 0.3 cm) from the strips used in color measurements were placed at right angles to the blade. The texture analyzer was set with a 5-g load cell and a crosshead speed of 200 mm/min.

Proximate compositions and moisture to protein ratio (MPR)

The proximate composition of jerky samples was determined from fresh (1 d) samples only, which was analyzed using the Association of Official Analytical Chemists Official Methods.^[10] MPRs were also calculated as the average percent moisture divided by the average percent protein in fresh (1 d) samples jerky.

Water activity and pH measurements

The water activity and pH of cured an uncured chevon jerky samples were determined in triplicate during the 30 d storage. Each sample was minced into pieces approximately 1 mm² in size. The water activity of jerky samples was determined in triplicate with a chilled-mirror dew point water activity meter (Aqualab model 3TE, Pullman, WA, USA). Each minced sample (2.0 g) was then stirred into 10 mL of deionized water to measure pH (pH model 501, Orion Research, Inc., Boston, MA, USA).

TBARS

TBARS were determined in triplicate from cured or uncured jerky (10.0 g) stored for 1, 15, or 30 d according to the method of Shahidi et al.^[11] The absorbance of the extracted and prepared analyte was measured at 532 nm using a Shimadzu (Model UV-2401 PC) spectrophotometer (Shimadzu Corp., Columbia, MD, USA) during the TBARS analysis. TBARS were calculated from a standard curve of malondialdehyde (MDA) and expressed as mg MDA/kg sample.

Fatty acid compositions

Total lipids were extracted from each jerky samples (on days 1, 15, and 30 d of storage) by means of the chloroform/methanol (2:1 v/v) method of Lee et al.^[12] The extracted lipids were saponified and esterified according to the AOAC Official Method¹⁰ 969.33 for the preparation of fatty acid methyl esters (FAME). The prepared FAME were analyzed using a Thermo Electronic (Austin, TX, USA) gas chromatography (Model TRACE GC Ultra) equipped with an automatic sampler Model AS-3000 (Thermo Electronic Corp., Austin, TX, USA). A 0.25-mm i.d. with 0.25 µm film thickness by 60-m long fused silica SP-2380 capillary column (Supelco, Inc., Bellefonte, PA, USA) was used to separate the methyl esters which were detected with a flame ionization detector (FID), with the following conditions: injection temperature, 240°C; initial temperature, 130°C; 4°C/min up to 220°C; helium flow, 1.5 mL/min; and, split ratio of 30:1. The identification of individual FAME from the sample was done by matching their retention time with those of known FAME standards (Alltech Associates, Inc., Deerfield, IL; Sigma-Aldrich Corp., Bellefonte, PA, USA) and the relative weight percent of individual FAME in each sample was also calculated using their corrected areas according to the American Oil Chemists’ Society for fatty acid analysis.^[13]

Volatile flavor compounds

Flavor volatiles of chevon jerky samples were extracted by the solid-phase microextraction (SPME) method of Harmon^[14] as modified by Lee et al.^[12] A portion (5.0 g) of the minced jerky samples was transferred into a 20 mL vial and then sealed with a polytetrafluoroethylene silicon septum (Supelo, Inc., Bellefonte, PA, USA). The vial was heated on a SPME sampling stand using a heat/stir plate (Model PC-400; Corning Inc., NY, USA). The vial temperature was maintained at 45°C during SPME headspace sampling. The SPME fiber (polydimetylsiloxane-divinylbenzene and carboxen; Supelco, Inc., Bellefonte, PA) was inserted into the heated vial through the silicon septum and then exposed to the headspace for 20 min. Subsequently, the adsorbed volatiles were desorbed for 5 min by inserting the SPME needle and exposing the fiber directly into the injection port (230°C) of a gas chromatography (TRACE GC Ultra; Thermo Electron Corp., Austin, TX, USA). The volatiles were separated on a Supelcowax-10 capillary column (60 m × 0.32 mm i.d., 0.25 µm; Supelco, Inc., Bellefonte, PA, USA), and detected with a mass selective detector (Finnigan TRACE DSQ MS; Thermo Electron Corp., Austin, TX, USA). The injection port was in the splitless mode and helium gas was used as a carrier gas with a flow rate of 1.5 mL/min. The column temperature was programmed from 50 to 230°C (4°C/min) and held at 230°C for 10 min. The mass spectrometry was operated in the electron impact mode with electron energy of 70 eV, a multiplier voltage of 1100 V, and data collected rate of 1.5 scan/s over a range of m/z 40–450. The volatile compounds were identified by comparing their mass spectra and retention times with those from known standard compounds (Sigma-Aldrich Corp., Bellefonte, PA, USA) or comparing their mass spectra with those contained in a mass spectra library (Thermo Electron Corp., Austin, TX, USA). The volatile compounds were also extracted from the minced jerky samples and then analyzed with a Thermo Electron gas chromatography (TRACE GC Ultra; Thermo Electron Corp., Austin, TX, USA), equipped with a FID under the same column conditions described in the SPME and gas chromatography-mass spectrometry (GC-MS) method described previously, The concentration of individual volatiles from each sample was determined as the percentage of total area of the peaks in the GC chromatogram.

Microbial counts

A 10-g sample from either cured or uncured chevon jerky stored for 1, 15, or 30 d was aseptically removed from vacuum packages and the 3M^TM Petrifilm plate techniques were used to enumerate microbial loads on jerky samples as recommended by the manufacturer.^[15] Appropriate sample dilutions were inoculated on Petrifilm plates (3M^TM Microbiology Products, St. Paul, MN, USA) to determine E. coli and total coliform (3M™ Petrifilm^TM E. coli/Coliform Count Plates), yeast and mold (3M™ Petrifilm^TM Yeast and Mold Count Plates), and aerobic plate counts (3M™ Petrifilm^TM Aerobic Count Plates) as prescribed by the supplier. Microbial colonies were counted and expressed as colony forming units (CFUs) per gram of sample.

Sensory evaluation

On days 1, 15, and 30 of storage, chevon jerky strips, prepared either with or without sodium nitrite, were removed from vacuum packages and cut into 2 cm long strips (2 × 2 × 0.3 cm) for sensory evaluations. Ten experienced panelists were seated in individual booths and presented four jerky samples (three strips/sample) in random orders on paper plates coded with 3-digit random numbers. Samples were evaluated on 8-point scales with 1 “dislike extremely” and 8 “like extremely” for color, flavor, texture, and overall acceptability.^[16] Panelists rinsed their mouths with room temperature bottled spring water between samples.^[17]

Statistical analysis

All data were analyzed as a randomized block design (RBD), blocked on day, with factorial treatment arrangement using the MIXED SAS procedure (SAS Institute Inc., Cary, NC), USA. The effects of processing treatment (with or without NaNO₂) and storage time (1, 15, and 30 d), as well as their interaction were considered to be fixed. Significant differences among means were determined by the least-squares means generated and statistically separated using the p-values for difference (PDIFF) option, protected by the analysis of variance (ANOVA) F-test (p ≤ 0.05).

Results and discussion

Physical properties of restructured chevon jerky

Color measurement

Cured chevon jerky had a higher (p < 0.01) Commission International de I’Eclairage (CIE) a*-value (14.24 versus 8.17) than uncured chevon jerky. Furthermore, CIE a*- and b*-values of the jerky were influenced (p < 0.01) by storage time. The CIE a*-values of the jerky were significantly (p < 0.01) decreased after storing for 30 d. Compared to the fresh jerky (d 1), the CIE b*-values (yellowness) of the jerky were also decreased (p < 0.01) over 30 d storage with some variations. A significant (p < 0.01) interaction was found between processing treatment and storage time for CIE a*-values. The CIE a*-values of the cured jerky were decreased (p < 0.01) over the first 15, but a*-value increased (p < 0.01) in the uncured jerky. No further changes were observed in the CIE a*-values of the jerky after 15 d. Compared to uncured jerky, cured jerky might be more acceptable to the consumer because of development of a desirable red color.^[18] Cured meat color develops in a series of complicated reactions until nitric oxide (NO)-myglobin is formed. Subsequently, the heat stable cured color complex such as nitrosylhemochromogen is developed by heating NO-myglobin. However, this heat stable cured color fades upon exposure to ultraviolet (UV) light. Furthermore, several intrinsic and extrinsic factors affect nitrite curing reactions such as meat system, pH, the amount of reductants present, temperature and time.^[19] In the present study, the redness (CIE a*-values) of cured chevon jerky decreased over 30 d storage under fluorescence light, which could be explained by cured color fading over the time of storage. Processing treatment and interaction of processing treatment and storage time significantly (p < 0.01) affected the hue angle values of jerky samples; however, storage time did not influence (p > 0.1) hue values. Cured jerky samples had a lower (p < 0.01) hue value (42.88 versus 60.83) than uncured samples. The hue values cured jerky samples increased (p < 0.01) at day 30. However, the hue values uncured jerky samples decreased (p < 0.01) over the first 15 d of storage, but values did not change changed (p > 0.05) thereafter. Processing treatment and storage time, as well as their interaction significantly (p < 0.01) affected the chroma values of jerky samples. Cured jerky sample had a higher (p < 0.01) chroma value (19.44 versus 16.92) than uncured samples; moreover, the chroma values of jerky samples decreased (p < 0.01) as the storage time progressed. The chroma values of cured jerky decreased (p < 0.01) over the 30 d of storage; however, the uncured jerky decreased (p < 0.01) the chroma values only over the first 15 d of storage but values did not change thereafter.

Instrumental texture measurement

The Warner-Bratzler shear force (WBSF) values of chevon jerky (5.58 to 6.03 ± 0.522 kg) were not influenced (p > 0.1) by processing treatments. However, storage time significantly (p < 0.01) affected on the WBSF values of chevon jerky (5.44 to 6.36 ± 0.390 kg). A significant (p < 0.01) interaction between processing treatment × storage time was determined for WBSF values of chevon jerky. Cured chevon jerky had decreased (p < 0.01) WBSF values over the first 15 d of storage, but then stabilized up to 30 d, whereas the WBSF values of uncured jerky did not change throughout the 30 d storage period. Similar results were reported by Yang et al.,^[20] who found that the shear force values of cured whole muscle beef jerky samples decreased during storage.

Chemical properties of restructured chevon jerky

Proximate composition and MPR

No differences (p > 0.1) were found in the proximate compositions of jerky prepared with or without sodium nitrite. Cured and uncured chevon jerky were determined to contain 47.7 and 46.9 ± 1.63% protein; 33.5 and 34.1 ± 2.34% moisture; 11.0 and 10.5 ± 0.26% ash; and 6.21 and 6.72 ± 0.438% lipid, respectively. In general, commercial intermediate moisture meat products contain 20–40% moisture^[21] and the restructured chevon jerky produced in the current study was also within that range. Based on the proximate compositions of chevon jerky samples, the average MPR values did not exceed 0.75; therefore, the restructured chevon jerky satisfied the United State Department of Agriculture (USDA)-Food Safety and Inspection Service (FSIS) standard of identity for jerky products (MPR ≤ 0.75:1).

Water activity (a_w) and pH measurements

There were no significant differences in the water activity (a_w) of cured and uncured chevon jerky (0.85 and 0.86, respectively). However, a_w values were influenced (p < 0.01) by the storage time. The a_w of chevon jerky samples increased (p < 0.01) over the first 15 d of storage, but did not change thereafter. The a_w of jerky samples varied from 0.84 to 0.87 within a 30 d of storage. Water activity (a_w) value less than 0.85 should control growth of all pathogenic bacteria of concern. USDA guidelines require that jerky products have an a_w value of ≤0.80 to be considered as shelf-stable.^[22] The resulting jerky products should be microbially safer, but might have unacceptable textures and flavors. In the present study, the a_w of fresh chevon jerky (day 1) was within the range of 0.84–0.85. Such jerky products require additional hurdles such as low pH, preservatives, reduced oxidation-reduction potential, and vacuum packaging, to extend shelf life with excellent storage stability.^[23] Processing treatment × storage time interactions and processing treatment did not affect (p > 0.1) the pH values (6.43 to 6.62 ± 0.040) of chevon jerky samples; however, storage time did influence (p < 0.05) pH values. The pH values of jerky samples increased over the 30 d storage with some variation, and ranged from 5.73 to 5.91. According to Jose et al.,^[21] intermediate-moisture meat products with a_w ranging from 0.6 to 0.9, had a broad range of pH values from 4.72 to 6.73. Yang et al.^[20] reported that the pH values of cured whole muscle beef jerky varied from 5.53 to 5.80, which were similar to those observed in chevon jerky manufactured in this present study.

TBARS

Significant (P < 0.05) differences were found in the TBARS values for jerky prepared with or without sodium nitrite. The uncured jerky had higher (p < 0.05) TBARS numbers (6.81 versus 6.26 ± 0.189 mg MDA/kg) than cured products. However, neither storage time nor processing treatment × storage time interaction influenced (p > 0.1) the TBARS values in jerky samples. One of the most noticeable benefits from nitrite addition was to extend shelf life of processed meat products by retarding the development of oxidative rancidity. The reaction of MDA with 2-thiobarbituric acid (TBA) is widely used for measuring the extent of oxidative deterioration of lipid in muscle food.^[24] In general, free radicals are derived from lipid oxidation, which may lead to the oxidation of meat pigments and the development of rancid odors and flavors.^[25] In the present study, lipid oxidation of chevon jerky was inhibited by incorporation of sodium nitrite. Compared with cured whole muscle beef jerky, chevon jerky had a higher range of TBARS values (4.0 to 4.8 versus 3.5 to 3.7 mg MDA/kg) over the 30 d of storage at ambient temperature.^[20] This may be due to higher concentrations of unsaturated fats in chevon and also due to differences in the processing of jerky such as temperature, time, oxygen exposure, oxygen removal, and antioxidant addition. According to Yang et al.,^[20] the TBARS values of the cured beef and pork jerky increased as the storage time progressed. However, this trend was not followed in the present study, and this may be due to the differences in oxygen pressures within packs of jerky because the beef and pork jerky was packaged without vacuum in the previous studies. It is generally accepted that TBARS values increase in meat with increasing storage time.

Fatty acid compositions

Twenty-eight fatty acids were identified in lipids extracted from the jerky samples, which consisted of 10 saturated (C10:0, C12:0, C13:0, C14:0, C15:0, C16:0, C16:0I, C17:0, C18:0, and C20:0), seven monounsaturated (C14:1n5, C16:1 trans, C16:1n7, C17:1n8, C18:1 trans, C18:1n9, and C20:1n9), and 11 polyunsaturated (C18:2 iso 1, C18:2 iso 2, C18:2 iso 3, C18:2n6, C18:3n3,C18:3n6, C20:3n6, C20:4n6, C20:5n3, C22:5n3 and C22:6n3) fatty acids (Table 1). Among the saturated fatty acids (SFAs), neither processing treatment nor storage time significant (p > 0.05) influenced the percentage weight of individual SFA; moreover, there were no significant (p > 0.05) interactions found between processing treatment and storage time. Similar trends were also found for individual monounsaturated fatty acids (MUFA) and polyunsaturated fatty acids (PUFA). The major four fatty acids in jerky were palmitic (C16:0), stearic (C18:0), oleic (C18:1n9), and linoleic (C18:2n6) acids, which accounted for 81.7 and 84.6% of total fatty acids in cured and uncured fresh jerky (d 1) samples, respectively.

Table 1. Fatty acid profiles of restructured chevon jerky prepared with or without sodium nitrite (NaNO₂) stored under fluorescent light for 30 d at ambient temperature.

	Without NaNO2			With NaNO2
Fatty acid, %	1 d	15 d	30 d	1 d	15 d	30 d	SE
C10:0	0.12	0.10	0.12	0.14	0.14	0.13	0.017
C12:0	0.21	0.21	0.23	0.29	0.27	0.24	0.039
C13:0	0.06	0.06	0.07	0.08	0.07	0.08	0.007
C14:0	2.75	2.71	2.78	3.58	3.05	2.96	0.305
C14:1n5	0.27	0.24	0.26	0.30	0.27	0.26	0.018
C15:0	0.70	0.67	0.71	0.81	0.71	0.70	0.046
C16:0I	0.23	0.22	0.22	0.27	0.22	0.23	0.015
C16:0	22.10	21.77	21.72	25.49	22.33	22.30	1.144
C16:1 trans	1.45	1.38	1.46	1.68	1.25	1.45	0.090
C16:1n7	1.08	0.99	1.04	1.28	1.08	1.07	0.088
C17:0	0.48	0.47	0.48	0.55	0.46	0.47	0.048
C17:1n8	0.58	0.53	0.53	0.60	0.55	0.54	0.038
C18:0	24.28	24.81	24.53	27.64	24.42	24.46	1.059
C18:1 trans	3.76	3.52	3.39	3.70	3.50	3.63	0.165
C18:1n9	33.70	31.41	33.80	23.74	31.77	31.79	3.162
C18:2 iso1	0.93	1.01	0.97	0.95	0.97	0.99	0.022
C18:2 iso2	0.41	0.37	0.38	0.44	0.35	0.40	0.033
C18:2 iso3	0.41	0.39	0.41	0.46	0.40	0.39	0.025
C18:2n6	4.50	5.09	4.95	4.87	4.87	4.74	0.212
C18:3n3	0.65	0.67	0.73	0.75	0.70	0.68	0.066
C18:3n6	0.11	0.10	0.12	0.12	0.09	0.10	0.008
C20:0	0.69	0.61	0.68	0.69	0.63	0.63	0.046
C20:1n9	0.17	0.18	0.20	0.17	0.19	0.17	0.019
C20:3n6	0.10	0.10	0.12	0.11	0.11	0.11	0.013
C20:4n6	1.18	1.44	1.47	1.26	1.43	1.37	0.151
C20:5n3	0.17	0.19	0.21	0.19	0.20	0.19	0.108
C22:5n3	0.10	0.09	0.10	0.09	0.09	0.08	0.013
C22:6n3	0.40	0.45	0.50	0.45	0.45	0.46	0.056

Within a row, least squares means that do not have a common letter differ (p < 0.05).

Current recommendations are that the PUFA:SFA ratio should be around 0.45.^[26] The PUFA:SFA ratios in the current study were lower than the recommended ratio, being 0.16 for cured-, and 0.17 uncured-fresh jerky (d 1) samples. The SFA such as lauric (C12:0), myristic (C14:0), and palmitic (C16:0) acids raise the low density lipoprotein-cholesterol concentrations in blood, and increase the risk of cardiovascular disease.^[27] These three SFA comprised 29.4 and 25.1% of total fatty acids in the cured and uncured fresh jerky (day 1) in this present study, respectively. Nutritional guidelines have suggested that the consumption of saturated and trans-fatty acids needs to decrease and the consumption of n-3 PUFA is required to increases in order to achieve a n-6/n-3 ratio in the diet of approximately 5:1 or less.^[28] The ratio of n-6/n-3 PUFA in fresh jerky prepared with or without sodium nitrate were 4.30 or 4.46, respectively, in the present study. In general, fats from goat meats are higher in PUFA such as linoleic (C18:2n6), α-linolenic (C18:3n3), and arachidonic (C20:4n6) acids, than those from other red meats.^[29] Hence, jerky from goat meat (chevon) might be more susceptible to lipid oxidation than that from beef because of a higher concentration of PUFA in chevon.

Sodium nitrite can act as an antioxidant to delay the development of oxidative rancidity. This prevention occurred in the present study according to the TBARS values determined between cured and uncured chevon jerky samples (4.26 and 6.81 mg MDA/kg, respectively). Consequently, higher concentrations of PUFA such as linoleic (C18:2n6), α-linolenic (C18:3n3), and arachadonic (C20:4n6) acids in cured jerky were expected because of the protective effect of adding nitrite in terms of stabilizing polyunsaturated fats. However, such an effect was not found in the present study. The degree of lipid oxidation is related to not only the amounts of unsaturated fats present but also other processing factors such as temperature, time, oxygen exposure, oxygen removal from packs, and the addition of antioxidants and/or reducing agents.^[30]

Volatile flavor compounds

About 40 peaks were detected in the restructured chevon jerky prepared with or without sodium nitrite. However, nearly half of these peaks were tentatively identified as either siloxanes or silanes which originated from the SPME-fiber and GC-column. Only twenty-one flavor volatiles were identified, which were divided into five groups according to their chemical families: 13 hydrocarbons, one acid, one ketone, two aldehydes, and four alcohols (Table 2). With regards to the group of compounds extracted from the fresh jerky (day 1), hydrocarbons constituted the major group with a similar percentage of total area in cured and uncured jerky samples (66.2 and 69.4%, respectively). Individual volatile compounds in the hydrocarbon group were not affected (p > 0.1) by processing treatments and storage times, as well as their interactions. Of the hydrocarbons, remarkably high proportions and numbers of terpenes were found in the jerky samples. Furthermore, 6 terpenes (α-pinene, β-pinene, β-phellandrene, 3-carene, 1-limonene, and α-cubebene) represented 57.7 and 62.37% of the total flavor volatiles from cured and uncured fresh jerky (day 1) samples, respectively. In general, a relatively high amount of terpenes are presented in spiced dry-cured products because of spices added during processing and accumulation in fat depots from animals’ diet.^[31] However, most terpenes from cured products have a very limited role in the intensity and variety of aroma threshold.^[32] Several of the volatile terpenes were detected in the jerky samples which might be originated from the added spices. Monoterpene hydrocarbons such as α-pinene, β-2-pinene, and 1-limonene, as well as sesquiterpene hydrocarbons such as α-cubebene, (E)-caryophyllene, α-copaene, and α-elemene were detected in the cured products prepared with sage and rosemary essential oils.^[33] However, (E)-caryophyllene and 1-limonene might be also derived from accumulation in fat depots from animal fed with grasses^[34] and oilseeds,^[31] respectively. According to Mottram,^[35] 1-limonen, β-pinene, (E)-caryophyllene, and 3-carene were derived from black pepper which were used as ingredients in cured products.

Table 2. Flavor volatiles isolated from restructured chevon jerky prepared with or without sodium nitrite (NaNO₂) stored under fluorescent light for 1, 15, or 30 d at ambient temperature.

	Without NaNO2			With NaNO2
Flavor volatile, %	1 d	15 d	30 d	1 d	15 d	30 d	SE
Hydrocarbons
Eicosane	0.08	0.11	0.10	0.10	0.12	0.15	0.022
α-Pinene	7.88	9.85	6.53	6.79	8.45	6.95	1.106
β-Pinene	6.69	6.24	7.14	7.54	6.24	7.44	1.168
β-Phellandrene	10.90	9.87	12.89	11.95	10.13	15.23	2.672
Carene	10.92	7.70	8.13	9.41	7.81	7.11	2.789
Limonene	19.68	19.64	16.82	15.62	19.28	13.5	2.877
Cubebene	6.30	6.80	6.39	6.41	7.30	6.82	1.259
Naphthalene	0.31	0.48	0.31	0.36	0.34	0.37	0.031
Elemene	1.62	1.47	1.17	2.07	1.94	1.18	0.357
Coparene	1.32	1.35	1.89	1.64	1.55	1.71	0.320
Caryophyllene	0.09	0.11	0.10	0.13	0.10	0.15	0.021
Cyclohexandiene	2.43	2.30	1.38	2.67	2.64	1.38	0.321
β-Guaiene	1.14	1.37	1.95	1.52	1.46	2.15	0.390
Acids
Acetic acid	0.06	0.09	0.12	0.08	0.08	0.14	0.033
Ketones
Octanone	9.03	8.93	10.31	11.50	10.06	12.40	1.703
Aldehydes
Nonanal	14.23	16.23	16.82	14.03	14.17	14.98	2.913
Benzaldehyde	0.80	0.77	0.96	0.81	0.73	0.98	0.098
Alcohols
Ethyhexanol	1.14	1.37	1.95	1.52	1.46	1.85	0.359
Terpinol	1.62	1.47	1.17	2.07	1.94	1.18	0.379
Spathulenol	1.63	1.34	1.89	1.64	1.56	2.07	0.326
Eugenol	1.43	1.75	1.39	1.79	2.02	1.63	0.402

Within a row, least squares means that do not have a common letter differ (p < 0.05).

Aldehydes represented about 15.0% of the total flavor volatiles from fresh chevon jerky (day 1), which were numerically the second largest chemical group after the hydrocarbons. Neither mean concentrations of nonanal nor benzenaldehyde were affected (p > 0.1) by processing treatments and storage times, as well as their interactions. Most aldehydes are derived from the oxidation of unsaturated fatty acids such as ocatanal, nonanal, and t-2-decanal from oleic acid (C18:1n9), pentanal, hexanal, heptanal, t-2-heptenal, t-2-octenal, and t-2-nonenal from linoleic acid (C18:2:n6), and t-2-pentenal, t-2-hexenal, 2-n-pentylfuran, and benzaldehyde from α-linolenic acid (C18:3n3).^[32] In the present study, nonanal and benzaldehyde were isolated and analyzed, whereas only nonanal was detected with a noticeable percent concentration in the jerky samples because of a higher amount of C18:1n9 in the jerky samples (Table 1).

Acids and ketones consisted of 0.1% and 9.0 to 11.5% of total volatiles, respectively, in fresh chevon jerky (day 1) samples. Neither average concentrations of acetic acid nor 3-octanone were affected (p > 0.1) by processing treatments and storage times, as well as their interactions. Acetic acid was the only acid positively identified in the present study. Acetic acid primarily originates from the microbial metabolism of carbohydrates.^[36] According to previous research on the dry-cured products, straight and branch chain aliphatic acids were derived from the hydrolysis of triglycerides and phospholipids,^[37] and the microbial activity on the surface of the meat,³⁸ respectively. In dry-cured meat products, ketones are generally formed through either lipid oxidation or microbial fermentation.^[32] Furthermore, straight-chain ketones are derived from either oxidation or thermal degradation of fatty acids.^[32,^38] However, a limited number of ketones were detected in chevon jerky samples.

Alcohols represented approximately 7.0% of the total flavor volatiles in fresh jerky (day 1) samples. Individual volatile compounds in the alcohol group were not affected (p > 0.1) by processing treatments and storage times, as well as their interactions. Most of the alcohols isolated from the jerky samples were oxygen-derivative terpenes such as α-terpinenol, eugenol, and spathulenol, which are commonly used in the food industry as flavor ingredients.^[33,^39] Furthermore, these three terpene alcohols have characteristics flavor notes such as pine smoke, spicy and clover-like, and earthy-aromatic odor and bitter-spicy taste, respectively.

Remarkably high numbers of volatile compounds were found in the dry-cured hams and sausages which were categorized into the 15 volatile groups: aromatic and aliphatic hydrocarbons, aliphatic and aromatic aldehydes, aliphatic ketones, aliphatic alcohols, carboxylic acids, ethers, esters, furans, phenols, and terpenes, as well as nitrogen, sulfur, and chloride compounds.^[33,^37] However, compounds such as these were not completely extracted using the SPME technique in the present study. Higher variability of volatile compounds found in the chevon jerky and other cured products (hams and sausages) may be explained by differences in ingredients (spices and meats) usage and processing technologies to develop the proper flavor of cured products. Volatile compounds from each meat matrix system are different, and even the volatile profiles from each muscle are not exactly the same.^[40] Furthermore, the type of a SPME fiber selection might also influence the quantitative and qualitative analysis of volatile compounds.

Microbial counts of restructured chevon jerky

No significant differences (p > 0.05) were detected on the aerobic plate counts from cured and uncured chevon jerky samples (4.10 and 4.27 ± 0.584 log CFU/g). However, the aerobic plate counts in jerky samples steadily increased (p < 0.01) with storage time. Coliform and E. coli, as well as yeast and mold, were not detected in the present study. Nitrite is added to control spore-forming pathogenic bacteria, most likely Clostridium botulinum. Bayne and Michener^[41] reported that no effect on the control of naturally occurring spoilage bacteria present in frankfurters whether or not nitrite was included. In the present study, the aerobic plate microbial counts of fresh jerky (day 1) were within a range of low level from 10¹ to 10² CFU/g. The low microbial levels determined in this study were anticipated due to low water activity (a_w < 0.85) associated with jerky products. However, the total microbial counts increased with storage time in chevon jerky whether or not nitrite was included. This may due to the progressively increase in water activity (0.84 to 0.87) and pH (5.73 to 5.91) of the jerky during 30 d storage.

Sensory properties of restructured chevon jerky

The sensory properties of chevon jerky prepared with or without sodium nitrite over the 30 d storage period are presented in Table 3. Cured jerky samples had higher (p < 0.05) sensory scores for color and flavor attributes than uncured equivalents. Furthermore, cured jerky tended (p = 0.08) to have a higher overall acceptability compared to uncured jerky. However, subjective texture properties of jerky samples were not influenced (p > 0.1) by processing treatment. All four sensory attributes of chevon jerky were not influenced (p > 0.1) by storage time. However, a significant (p < 0.05) processing treatment × storage time interaction was observed with respect to the color of jerky samples. Cured jerky samples had a higher (p < 0.05) mean color score than uncured samples over 30 d storage. Color is a critical importance fact for consumer acceptance of meat products and nitrite is responsible for the fixation of a desirable shaded pink color.^[18] In the present study, sensory panel members clearly differentiated between the color of cured and uncured chevon jerky, and preferred cured jerky color compared to uncured equivalents. According to the instrumental color measurements, cured jerky had a higher CIE a*-value (redness) than uncured jerky (14.24 versus 8.17. Another important function of nitrite is creating a unique flavor profile that is distinguished from products not containing nitrite.^[19,42] Sensory panel members easily detected the difference in flavor between chevon jerky samples prepared with or without sodium nitrite. However, the noticeable flavor difference determined by sensory evaluation was not detected by the chemical analysis of volatile compounds in cured and uncured chevon jerky samples (Table 2). Numerous efforts to identify flavor compounds unique to cured meat product have had limited success. Ramarathnam^[30] proposed that a clear flavor difference between products prepared with or without nitrite was due to the reduction of lipid oxidation in products containing nitrite. Moreover, sensory research also suggested that cured flavor was derived from a combination of a complex cured flavor with a lack of rancid flavors.^[43]

Table 3. Changes in sensory properties of restructured chevon jerky prepared with or without sodium nitrite (NaNO₂) during 30 d of storage at ambient temperature under fluorescent light.

	Without NaNO2			With NaNO2
Sensory parameter	1 d	15 d	30 d	1 d	15 d	30 d	SE
Color	5.70^b	5.41^b	6.84^b	7.23^a	7.36^a	7.61^a	0.330
Texture	7.97	6.59	7.90	7.73	6.25	7.88	0.401
Flavor	6.28	6.28	6.27	7.48	7.83	7.89	0.211
Overall	6.40	6.78	6.43	7.65	7.86	7.96	0.309

Within a row, least squares means that do not have a common letter differ (p < 0.05).

Conclusions

Generally, either nitrate or nitrite is added to processed meat products to develop color and flavor characteristics associated with cured meats, as well as controlled the oxidation of lipid and microbial growth. Adding of sodium nitrite to jerky product formulation significantly improved color and sensory properties, as well as control the lipid oxidation of chevon jerky; however, the reduction in lipid oxidation did not impact on the fatty acid and flavor profiles of jerky products. Furthermore, compounds responsible for cured flavor differences were not determined from volatile compounds extracted from the chevon jerky as determined by SPME methodology.