Effect of Water Activity, Yuza ( Citrus junos Sieb. ex Tanaka) Powder and the Mixture of Sodium Lactate and Sodium Acetate on Quality and Safety in Beef Jerky

Despite its low water activity (A w ), food poisoning accidents associated with beef jerky consumption and problems due to mold growth have been reported. The objects of this study were to investigate the effect of yuza powder and the mixture of sodium lactate (SL) and sodium acetate (SA) to prevent the growth of S. aureus and A. flavus, as well as aflatoxin production in beef jerky. Different concentrations of the SL and SA (0, 0.75, and 1%) mixture were added to sliced beef and the A w s were adjusted to 0.70, 0.75, and 0.80. The effect of yuza powder and the SL and SA mixture on S. aureus in beef jerky (A w 0.80) was also investigated at 10˚C and 25˚C. A rapid decline is that S. aureus population was observed in beef jerky containing yuza powder and mixtures of SL and SA. Antifungal effects against A. flavus were observed in beef jerky containing the SL and SA mixture at A w below 0.75. The growth of A. flavus and aflatoxin production were prevented in beef jerky containing the yuza powder and a 1% mixture of SL and SA at 10˚C and 0.80 A w . The addition of yuza powder increased the hardness score of the beef jerky. Under current A w regulations (0.80), beef jerky may pose a public health risk due to the growth of A. flavus and the presence of aflatoxin.

as well as the flesh of yuza, can be used as food ingredients. Yuza is consumed with tea, where the sliced yuza peel and flesh are sugared and made into a marmalade-like syrup sweetener. Currently, yuza has received attention as a healthy food ingredient from natural plants. Yuza fruit contains vitamin C, dietary fiber, beta-carotene, flavonoids, and limonoids, which cause a bitter taste. New product development efforts using yuza's peel and flesh residue have been reported [13]. The antimicrobial effects of other citrus fruits, such as grapefruit [14] and oranges [15] have also been reported. But yuza's antimicrobial and antifungal effects have not yet been investigated.
Opti.Form Powder Ace S50 contains a 5:5 mixture of sodium lactate (SL) and sodium acetate (SA), produced by fermentation from sugar. It is also known to extend the shelf life of meat products [16]. Various concentrations of sodium (di) acetate and sodium lactate mixtures have been used to prevent spoilage and the growth of pathogenic bacteria in meat products [17] [18]. Lactate alone (1.5% to 3%) or in a mixture of 0.125% to 0.25% diacetate (wt/wt) has been used in ready-to-eat (RTE) meats as antimicrobial additives [19].
In this work, we investigated the effects yuza powder and the mixture of sodium lactate and sodium acetate on the physicochemical, antimicrobial, antifungal, and aflatoxin-inhibiting properties of beef jerky as functions of A w and temperature.

Preparation of Dried Yuza Powder
Yuza was purchased in Corporation StoreFarm (Goheung, Korea) and washed with tap water. The washed yuza was cut in half and was squeezed to exclude juice. Then, the squeezed yuza halves were dried in a dried oven (HFD-6000HL, Hanil, Seoul, Korea) at 55˚C for 24 h. Dried yuza was grounded in a blender (HR2870/00, Philips, Armsterdam, Netherland) as a powder, which was stored at −20˚C until it is being used.

Inoculum Preparation
The Staphylococcus aureus (

Preparation of Beef Jerky
Sliced beef (0.7 cm thickness) was purchased from a local market (MangWon market, Seoul, Korea) and marinated with 15% sugar and 10% soy sauce with 0 (control) or 1.5% yuza powder.

Inoculation of S. aureus and A. flavus onto Beef Jerky
Beef jerky was cut into 5 g pieces using sterilized scissors and forceps and put

Survival Model
The survival curves were generated and iteratively fitted to the Weibull equation  N 0 : log initial number of cells, t: time The Weibull model provides two parameters: delta which is referred to as a characteristic of time parameter and p is the shape parameter. The delta value is the time of the first decimal reduction concentration for part of the population.
A p value < 1 indicates a concave upward survival curve and p > 1 is a concave downward survival curve. If p = 1, the decrease is log-linear, which corresponds to a first-order decay reaction [20].

Effect of Yuza Powder on the Inhibition of Aflatoxin Production
A. flavus solution (100 µL) at a concentration of 10 6 -10 7 spores/mL was inoculated into beef jerky samples, which were either stored at 10˚C for eight weeks or at 25˚C for four weeks. At the end of each storage period, 25 mL of 70% methanol was added to 5 g of each sample, which was shaken on a rotary shaker at 140 rpm during 15 minutes. Then, the total aflatoxin quantity was estimated using the AgraQuant Aflatoxin Test Kit (Romer Labs, Getzersdorf, Austria).

Water Activity (Aw)
The water activity (A w ) of beef jerky was measured using a waster activity meter (AwTherm Rotronic, Hauppaugue, NY, USA) at 23˚C.

Instrumental Color Analysis
For color analysis of the beef jerky, the values of a* (redness), b* (yellowness), and L* (lightness) were measured using a colorimeter (Minolta CR-400, Osaka, Japan). Before sample measurements, the colorimeter was calibrated with a white standardization plate. All samples were cut into rectangular shapes (5 × 5 cm). The color of beef jerky was measured at five different parts of the sample.

Texture Profile Analysis
The beef jerky was cut into pieces (10 × 10 × 3 mm) and the texture was measured using a texture analyzer (CT-10K, Brookfield, Middleboro, MA, USA). A TA7 knife edge (60 mm) was used as a probe. Conditions for the texture profile analysis (TPA) of beef jerky were 2.0 mm/s for pre-test speed, 1.0 mm/s for test speed, and 5.0 mm/s for post-test speed with 70% deformation of the test target type and 10 g of trigger load. Texture profile analysis values, such as hardness, adhesiveness, cohesiveness, springiness, chewiness, and gumminess, were measured as described by the Bourne method [21].

Sensory Evaluation
In order to study the effect of yuza powder and the mixture of SL and SA on beef jerky, four kinds of beef jerky were prepared for sensory evaluation: 0.75 BJ

Statistical Analyses
All experiments were performed at least twice. The significance of the differences between the sample treatments was measured by one-way ANOVA, followed by Duncan's multiple range test (p < 0.05) using the SAS program (version 9.3, SAS Institute, Inc., Cary, NC, USA).

Effect of Water Activity and the Mixture of Sodium Lactate and Sodium Acetate on the Fate of S. aureus in Beef Jerky
Water activity affects the growth of bacteria. S. aureus may grow at A w values near 0.86 [22]. In order to investigate the effect of water activity and the SL and SA mixture on the behavior of S. aureus in beef jerky, 0.75 or 1% of the SL and SA mixture was added and the water activity of beef jerky was adjusted to 0.70, 0.75, and 0.80 and it was stored at 25˚C. The S. aureus population decreased in the original beef jerky, regardless of the A w values, and the reduction rate was affected by the water activity and the concentration of the SL and SA mixture ( Figure 2).
The delta value of S. aureus was the lowest at A w 0.75. The shape parameters (p) of all samples at 25˚C were p > 1 (data not shown), which corresponded to downward concavity ( Figure 2). This indicated that S. aureus in beef jerky displayed a long survival lag phase in the beginning but a rapid death at the end of 13 days of storage at 25˚C. Regardless of the presence of the SL and SA mixture, S. aureus in beef jerky at A w 0.70 survived longer than that at A w 0.75. According to the work by Ingham and others [23], S. aureus and L. monocytogenes in vacuum packaged beef jerky rapidly decreased at A w 0.87 compared to A w 0.63, suggesting that other factors, such as seasoning, smoke compounds, besides A w affected S. aureus behavior. A recent study reported that S. aureus grew in commercial aerobically packaged beef jerky with an A w of 0.78 at temperatures above 21˚C [7].
In addition, the effect of the 5:5 mixture of SL and SA on S. aureus in beef   Listeria monocytogenes in ready-to-eat meat products at 4˚C for three months [24]. Most previous studies on the antimicrobial effect of lactate and diacetate have concentrated on L. monocytogenes in meat products. Since beef jerky is manufactured by a manual process, the risk of S. aureus due to cross-contamination during manufacturing should not be ignored and control measures for the safety of beef jerky must be implemented during the manufacturing process.

Effect of Water Activity and The mixture of Sodium Lactate and Sodium Acetate on the Fate of A. flavus in Beef Jerky
In the commercial market, various beef jerkies are sold in aerobic or anaerobic packages and, thus, fungal growth occurs easily in aerobically packaged jerky [8].
Nitrite is added to jerky to control bacterial growth [25]. However, nitrites do not prevent the growth of fungi [11]. In this study, the ability of A w and the SL and SA mixture to control the growth of A. flavus in beef jerky at 25˚C for four weeks was investigated ( Figure 3). The growth of A. flavus in beef jerky containing the SL and SA mixture was inhibited at 25˚C for four weeks, regardless of the A w , indicating that addition of the SL and SA mixture to beef jerky had an antifungal effect. Without the SL and SA mixture, at A w above 0.75, the growth of A. flavus in beef jerky lagged for 2 weeks, then increased over 6 log CFU/g, while the growth of A. flavus was not observed for four weeks at A w 0.70. The synergistic effect of a low A w and the SL and SA mixture on A. flavus inhibition was stronger than when water activity alone was varied or the SL and SA mixture alone was used to control the A. flavus growth. The results of this study indicate that the growth of A. flavus cannot be controlled only by adjusting water activity and that various techniques, such as temperature control and antifungal agents, must be used. A. flavus in jerky has also been controlled by vacuum packaging [10], radiation [10] and flexible thin-layer plasma [4]. The addition of sodium lactate, followed by storage at 4˚C also inhibited the growth of mold and yeast in traditional meat products in Turkey [26]. The addition of 2% sodium lactate to vacuum packaged sausage inhibited the growth of mold and yeast for eight days at 8˚C [27]. These results indicate that sodium lactate had an antifungal effect in these meats. Samapundo

Effect of Yuza Powder and the Mixture of Sodium Lactate and Sodium Acetate on the Fate of S. aureus in Beef Jerky at 10˚C and 25˚C
Yuza's peel and flesh residue have been tested in new product development investigations because of its numerous health benefits. In this work, the synergetic antimicrobial activity of yuza powder and the SL and SA mixture on S. aureus in beef jerky was investigated. Sliced beef was marinated with 1.5% yuza powder with and without the SL and SA mixture and was dried to adjust the water activity to 0.80. The amount of S. aureus in prepared beef jerky was investigated at 10˚C and 25˚C ( shortest delta values of S. aureus were observed in the 1.0% SL and SA mixture in beef jerky, which were accompanied by a long lag phase in the beginning, followed by a rapid death at the end of storage with a downward concave shape (p > 1). Overall, the populations of S aureus in beef jerky decreased faster at 25˚C compared to 10˚C, regardless of the presence of yuza powder or the SL and SA mixture. The worst condition for the survival of S. aureus was observed in beef jerky containing yuza powder and 1% SL and SA mixture at 25˚C. These results indicate that yuza powder had a synergetic antimicrobial effect with the SL and SA mixture. In commercial settings, beef jerky is sold at refrigerated or ambient temperatures. The settings at retail markets must be verified for the safety of beef jerky. The results of the present study showed that the addition of yuza powder and the SL and SA mixture to beef jerky decreased the populations of S. aureus at both 10˚C and 25˚C and, thus, reduced the risk of food poisoning that occurs from enterotoxin produced by S. aureus. Yuza peel consists of many compounds, such as limonene, hesperidin, and naringin [29]. Limonene has been shown to have an antimicrobial effect [30]. Although yuza contains these antimicrobial substances, studies on the antimicrobial properties of yuza have not been researched, unlike other citrus fruits. The results of this study showed that yuza can be used, not only as a flavor enhancer but also as an antimicrobial in processed meat products.

Effect of Yuza Powder and the Mixture of Sodium Lactate and Sodium Acetate on A. flavus and Total Aflatoxin Production in Beef Jerky at 10˚C and 25˚C
In order to investigate to antifungal activity of yuza powder and the SL and SA mixture on A. flavus and aflatoxin production in beef jerky, A. flavus was inoculated into beef jerky containing 1.5% yuza powder and 0.75% or 1% SL and SA mixture. The jerky was stored for eight and four weeks at 10˚C and 25˚C, respectively ( Figure 4). No growth of A. flavus in the beef jerky containing yuza powder and 1% SL and SA mixture was observed at 10˚C for eight weeks, while the growth of A. flavus was not prevented at 25˚C. The growth of A. flavus was also prevented in beef jerky containing 1% SL and SA mixture but the growth of A. flavus was not prevented with just yuza powder at A w 0.80 (Figure 3). The  most common cause of citrus fruit decay is mold [31]. In this work, the lag time of A. flavus in beef jerky containing just yuza powder without the SL and SA mixture was extended up to five weeks at 10˚C, indicating that storage at low temperature may decrease the risk of beef jerky due to the growth of A. flavus.
Aflatoxin production is affected by several environmental conditions, such as A w , CO 2 levels, temperatures, and incubation times [32] [33]. These results indicate that the optimum conditions for aflatoxin production varied depending on the environment. Figure 5 shows the effects of A w , yuza powder and the mixture of SL and SA on total aflatoxin production in beef jerky measured at 10˚C for eight weeks and 25˚C for four weeks. The water activity was the most important factor controlling aflatoxin production in beef jerky. Aflatoxin was not detected in any samples with an A w less than 0.75 (data not shown). However, the maximum accumulation of total aflatoxin (7.31 ppb) was observed in beef jerky without the SL and SA mixture at A w 0.80. Although aflatoxin accumulation in original beef jerky significantly declined with increasing amounts of the SL and SA mixture (0.75% and 1.0%) at A w 0.80, the addition of the SL and SA mixture did not completely prevent aflatoxin production in beef jerky. These results suggest that the A w of beef jerky should be maintained at less than 0.75 to avoid aflatoxin accumulation.  Although there is risk of of aflatoxin in beef jerky, regulatory aflatoxin limits in many countries have not set. The regulatory limit of total aflatoxin in nuts is 20 ppb in the US and Korea [34] [35]. In the present study, the total amount of aflatoxin in all beef jerkies was lower than the present regulatory limits for nuts of Korea. The range of water activity of commercial beef jerky in Korea has been reported to range from 0.70 to 0.83 [2] and aflatoxin may be produced during the shelf-life of beef jerky at Aw 0.80 or higher. Thus, regulations for the safe limit of water activity for beef jerky are needed and temperature control must be implemented at retail markets. Figure 5 shows the effect of yuza powder and the SL and SA mixture on total aflatoxin in beef jerky at A w 0.80 at 10˚C and 25˚C. The growth of A. flavus in beef jerky proceeded for eight weeks at 10˚C and four weeks at 25˚C. Then, when the storage period was over, the amount of aflatoxin in beef jerky was measured using the AgraQuant Aflatoxin Test Kit. There were significant differences in the amount of aflatoxin in the beef jerky samples that varied according to the concentration of the SL and SA mixture at both 10˚C and 25˚C, regardless of the presence of yuza powder. No aflatoxin production was observed in beef jerky containing yuza powder and 1% SL and SA mixture after eight weeks of storage at 10˚C. However, aflatoxin production by A. flavus was not prevented in beef jerky with an A w of 0.80 at 25˚C, regardless of the presence of yuza powder and the SL and SA mixture, indicating that these additives were not effective to prevent aflatoxin production at ambient temperatures. According to the results of the present study, the A w of beef jerky must be adjusted to 0.75 to prevent aflatoxin production at ambient temperatures. Overall, the amount of aflatoxin produced in beef jerky was lower than that containing yuza powder at 25˚C, regardless of the addition of the sodium acetate and sodium lactate mixture of. Since more growth of A. flavus in beef jerky containing yuza powder was observed, more aflatoxin was detected. Beef jerky is commercially sold refrigerated or at ambient temperature, which is the optimal temperature for A. flavus growth and aflatoxin production [36]. Several studies have shown that the concentration of aflatoxin B 1 in sorghum seeds increased at 37˚C compared to that

Effect of Yuza Powder and the Mixture of Sodium Lactate and Sodium Acetate on the Color and Texture of Beef Jerky
The effects of yuza powder and the SL and SA mixture on the color of beef jerky are shown in Table 2. Because brightness and redness of meat products are expected in meat products, the color of meat products is an important quality parameter. Addition of the SL and SA mixture significantly increased the lightness (L*), redness (a*), and yellowness (b*) of beef jerky (p < 0.05), regardless of the addition of yuza powder. The lightness of meat products is affected by many factors, including the concentration of additives [38], fiber content and type of meat products [39].

Effect of Yuza Powder and the Mixture of Sodium Lactate and Sodium Acetate on the Sensory Scores of Beef Jerky
In order to test the taste preference for beef jerky containing yuza powder and the SL and SA mixture, color, flavor, sweetness, bitterness, texture, and overall acceptability were evaluated by 70 non-trained panelists (Table 3). Overall, no significant differences were observed in the beef jerky with or without yuza powder and the SL and SA mixture. However, the parameters of sweetness and bitterness were significantly affected by the yuza powder, regardless of the addition of the SL and SA mixture. The addition of yuza powder to beef jerky reduced sweetness and increased bitterness, indicating that sweetness and bitterness might be affected by the unique taste and flavor of yuza powder. However, the change was very minimal and other sensory characteristics were not affected.

Conclusion
The results from this study demonstrated the antimicrobial effect of yuza powder and the SL and SA mixture in beef jerky. However, the growth of S. aureus was not controlled in beef jerky with an A w 0.80. In addition, yuza powder was not very effective in controlling the growth of A. flavus in beef jerky but the growth of A. flavus was controlled by the addition of 1% SL and SA mixture and aflatoxin production in beef jerky. Since aflatoxin was produced in all beef jerky with an A w of 0.80, the safe A w level of jerky in Korea (0.70 -0.83) must be reevaluated. The quality of beef jerky was also affected by the A w , yuza powder, and the SL and SA mixture. Color parameters (L*, a*, b*) were also enhanced by the addition of yuza powder and the SL and SA mixture. Hardness was increased by the addition of yuza powder. With the exception of sweetness and bitterness, no significant differences in sensory scores of the beef jerkies were observed between those with and without yuza powder. Scores for sweetness and bitterness of the beef jerkies containing yuza powder were higher than those of the other beef jerkies. The results of the present study indicate that yuza powder may be used as a new ingredient to create new tastes of beef jerky.