Influence of Storage Duration on Stability and Sensorial Quality of Dried Beef Product (Kilishi)

This study was designed to investigate the influence of storage duration on the stability and sensorial quality of kilishi samples. The conventional traditional kilishi (TK) and sausage-type (SK) at varying percentage of ingredients were processed. Chemical and sensorial analyses were performed to investigate quality changes and to determine the shelf stability of the kilishi samples stored at 28 ± 2°C for 150 days. The proximate, peroxide value (PV), free fatty acid (FFA) and thiobarbituric acid (TBA) were found statistically significant (P ≤ 0.05) in the kilishi samples throughout storage. The lowest PV (8.24 mEq/kg), FFA (3.12% oleic acid) and TBA (0.26 mgMDA/kg) were recorded in SK7 (115% ingredients), while the highest PV (35.11mEq/kg), FFA (11.18% oleic acid) and TBA (1.57 mgMDA/kg) occurred in SK2 (85% ingredients). Highest protein (55.84 ± 0.05%), fat (19.20 ± 0.09%) and ash (5.58 ± 0.08%) were obtained from SK7, SK2 and SK7 respectively and the organoleptic results showed that SK2 had the best acceptance and was significantly different (P ≤ 0.05) compared to the other kilishi samples. Influence of Storage Duration on Stability and Sensorial Quality of Dried Beef Product (Kilishi)


Introduction
Meat is an animal tissue used as food [1]. It is composed of tissue or muscle fibre cells, fat and connective tissue, it can also be composed of pieces of bone [2,3]. Meat plays an important role in nutrition as a contributor of high quality protein. However, meat is a highly perishable food item due to abundance of a number of nutrients that favor the establishment, growth and multiplication of microorganisms [4]. In the tropics, meat spoils quickly a few hours after the outset of rigor-mortis and post-mortem handling, hence meat needs to be preserved. A major meat preservation technique whose use dates back to records from 12 th Century is sun drying [5,6]. Today, a variety of sun-dried meat products exist. They include amongst others: the Pemmican that is prepared by exposing strips of lean meat to the sun, the Charqui, which is native to South American and Biltong found in South Africa [7]. In Nigeria, the dried meat product kilishi constitute one of daily delicacies and is equivalent to Pemmican and Charqui. Kilishi is a traditional sun dried Nigerian and Sahara African meat product processed using lean beef in combination with plant ingredients. It contains about 46% meat and 54% non-meat ingredients. A finished product contains about 50% protein, 75% moisture, 18% lipid and 9.8% fibre/ ash respectively [8,9]. It is a rich nourishing snack and a source of supplementary animal protein formulated using hurdle technology. Salting, dehydration or sun drying and packaging are hurdles applied in sequence to inhibit deteriorating microorganism [10]. Traditionally, Kilishi is prepared from boneless lean meat that is sliced in sheet of 2 mm thickness and partially dried in the sun followed by immersion in a slurry of ingredients before a second period of sun drying and brief roasting to stabilize the protein [11,12]. As a ready-to-eat convenience meat product, Kilishi possess an excellent shelf-life. According to Igene et al. [13] and Isah and Okubanjo [14], Kilishi has a shelf life of 12 months at room temperature. The ability of the product to keep for several months at room temperature is fast making the product a household name. This study therefore is aimed at evaluating the influence of storage duration on the stability and sensorial quality of Kilishi.

Sample preparation and processing
Meat preparation: The semitendinosus muscle of beef (9 kg) used for the study was trimmed of all visible fat, bone and connective tissue and then weighed. About 1kg of the resultant lean beef (8.2 kg) was sliced into thin sheets of 0.17 cm to 0.20 cm thick and 60 cm to 80 cm long along the fibre direction and dried for the traditional kilishi (TK). While 1 kg each of the remaining resultant lean beef will be comminuted with different percentage of the infusing ingredients to form the sausage-type kilishi (SK).

Preparation of infusing ingredients:
Infusion slurry was prepared following the procedures of Igene [8] using the ingredients as shown in Table 1. The fresh groundnut paste was prepared from grains of dry uncooked groundnut after extraction of oil by pressing. The various ingredients were ground and mixed thoroughly with water to form slurry. and spread out on flat steel trays on a raised platform till sun dried to generate the traditional kilishi. For the sausage-type kilishi, the meat was comminuted with various percentages of the infusing ingredients, spread into thin sheets of approximately 2mm thickness on steel trays, cut into long strips and dried. After drying, the traditional kilishi (TK) and respective sausage-type kilishi (SK) were roasted in an oven at a temperature of 100°C for 10-15min. Finally, the finished products were cooled at room temperature, packed and heat sealed in high density polyethylene (HDPE) bags and stored at ambient temperature (28 ± 2°C) for further analysis.

Storage stability and sampling
The traditional kilishi and sausage-type kilishi were stored for 150 days at ambient temperature and samples were drawn at specified days and subjected to proximate, chemical and organoleptic analysis.

Chemical analysis
The samples used for the analysis were assayed in duplicate. The moisture, protein, fat and ash contents of the kilishi samples were determined using the standard methods of AOAC [15] and Nielsen [16]. Peroxide value (PV), free fatty acid (FFA), and thiobarbituric acid (TBA) were determined according to the method described by Nielsen [16].

Organoleptic analysis
Organoleptic attributes of flavour, juiciness, tenderness, pungency and overall acceptability of the kilishi samples were evaluated by a 30-member in-house consumer panelist selected from among students and staff of Department of Food Science and Technology of the University. A 9-point hedonic scale was used with 9 for like extremely down to 1 for dislike extremely [17].

Statistical analysis
All the analysis was carried out in triplicates and data obtained were analyzed using analysis of variance (ANOVA) method. Where the variance ratio (F-values) proved significant, Fishers least significant difference (LSD) was used to separate the means.

Proximate composition
The proximate composition of the kilishi samples are presented in Table 2. There were significant differences (P ≤ 0.05) in all the proximate parameters evaluated. The moisture content of the kilishi samples ranged from 10.02% -12.02% with SK 6 having the highest moisture content of 12.02% and SK2 the lowest moisture content of 10.02%. The reduction in moisture content of SK2 is desirable as this can affect the quality of the sample positively in relation to other kilishi sample [12]. Generally, the moisture content of the kilishi samples indicates that the kilishi samples were sufficiently dried to minimize microbial growth though moisture values of 6.92%, 9.87% and 10.00% were recorded by Jones et al. [18], Apata et al. [12] and Olusola et al. [19] respectively. The protein content of the entire kilishi samples ranged from 51.62% in SK2 to 55.84% in SK7. The range of values obtained with regards to the crude protein content was similar to the values (53.41%-64.53%) reported by Isah and Okubanjo [14]. However, significant difference (P ≤ 0.05) occurred in the protein content of the kilishi samples. SK7 had the highest protein content (55.84%) and SK2 the lowest protein content (51.62%). The high crude protein content obtained can be attributed to the various ingredients utilized in the kilishi preparation and is in agreement with report by Igene et al. [9]. The fat content of the kilishi samples differed significantly (P ≤ 0.05) and ranged from 17.34% in TK to 19.20% in SK2. Generally, the fat content of the kilishi samples were high and this can be attributed to the groundnut cake powder which represent a considerable proportion of the product [13]. The ash content is an indicator of the mineral content of the meat. The ash content of the kilishi samples ranged from 4.54% in SK2 to 5.58% in SK7. The pattern of ash content observed in this study revealed that the higher the slurry infused into the meat during kilishi preparation, the higher the level of ash content in the product. This indicated that most of the ingredients in the slurry might have lost their mineral contents into the slurry hence, into the meat and product and this agrees with the report of Elizabeth [20] who observed that the ash content of any processed meat would be the content of the muscle tissue in addition to that of ingredients used.

Free fatty acid (FFA)
The FFA content in a product is an indication of the quality of the product. Lipid hydrolysis development strongly depends on the hydrolytic enzyme content and it is also influenced by different external and internal factors. The FFA content of the kilishi samples are presented in Figure 1. The FFA values ranged from 3.12%-11.18% oleic acid and the FFA content significantly increased (P ≤ 0.05) in all the samples during the 150 days of storage. However, SK2 showed higher FFA values and it is significantly different (P ≤ 0.05) when compared with the other kilishi samples. Also, it was observed that the FFA content of the kilishi samples decreased progressively as the percentage of ingredients used in processing the kilishi increases. SK7 had the lowest FFA content and SK2 the highest FFA content in all the storage days. This result obtained suggests that the various ingredients (concentration) used in processing of the kilishi samples especially the spices inhibited FFA production and is in agreement with the findings of Ogbonnaya and Imidobah [6] and Mgbemere et al. [21].

Peroxide value
The changes of peroxide value as primary products of lipid oxidation of the kilishi samples are shown in Figure 2. The PV content significantly increased (P ≤ 0.05) in all the kilishi samples during the 150 days storage and there were significant differences (P ≤ 0.05) among the samples. The highest value (35/11 mEq/kg) of peroxide was recorded for SK2 while the lowest value (8.24 mEq/kg) was observed in SK7. Also, it was observed that the PV content decreased progressively as the percentage of ingredients inclusion used in processing the kilishi samples increases. Since peroxides are inversely related to development if rancidity, it is inferential that the sample with the highest inclusion of ingredients, SK7 (115% ingredients) was the most effective in slowing down primary oxidation when compared to the other kilishi samples. This result is in agreement with report by Mgbemere et al. [21]. It also agrees with the studies of Siripongvutikorn et al. [22] that spices activities as antioxidant are directly related to their concentration.

Thiobarbituric acid (TBA)
TBA is a widely used indicator for the assessment of degree of secondary lipid oxidation. It evaluates the second stage of autoxidation during which the peroxides are oxidized to aldehyde and ketones which impart the disagreeable rancid odours and flavour. The effect of storage duration on TBA value of the kilishi samples stored at ambient temperature (28 ± 2°C) is shown in Figure 3. The TBA values increased in all the samples over time particularly in SK2. The initial TBA values ranged from 0.26 mgMDA/kg in SK7 to 0.33 mgMDA/kg in SK2. After 150 days of storage at 28 ± 2°C, the TBA values ranged from 0.97 mgMDA/kg inSK7 to 1.57 mgMDA/kg in SK2, thus indicating that TBA of SK7 increased by 0.71 mgMDA/kg, while the TBA of SK2 increased by 1.24 mgMDA/kg after 150days. This result indicates that high concentration of spices is effective in retarding lipid oxidation and is in agreement with reports by Siripongvutikorn et al. [22]. However, the results obtained are within the acceptable limits of the maximum level of TBA value, indicating good quality of the kilishi samples during storage, which is 1-2 mgMDA/kg lipid.

Organoleptic analysis
The organoleptic evaluation of food products to any food processing technology is very important in determining the consumer acceptability. The results of sensorial analysis for the kilishi samples stored at ambient temperature for 150 days are presented in Tables 3-6. The results obtained shows that there were significant variations (P ≤ 0.05) in all the sensory parameters evaluated. With regards to flavour, the highest flavor of 8.43 ± 0.56 for day one, 7.60 ± 0.36 for day 50, 6.30 ± 0.47 for day 100 and 5.55 ± 0.31 were observed in SK2. Physiologically, the perception of flavour involves the detection of four basic sensations including saltiness, sweetness, sourness and bitterness by the nerve endings of the surface of the tongue [23]. This result reveals that the flavour of SK2 was higher probably because the fat content of the product was relatively high and the moisture content was also low hence the high flavour of the product compared to the other kilishi samples and this is in conformity with the findings of Olusola et al. [19] and Apata et al. [12]. It also supports the observation of Melton [24] that as the fat of meat increases so does the flavour.
The tenderness of meat can be defined as the secondary manifestation of the structure of meat and the manner in which this structure reacts to the force applied during biting and the specific senses involved in eating [25]. It is how meat feels in the mouth during manipulation and mastication [19]. The result of tenderness of the kilishi samples as shown in Tables 3-6 shows that there were significant differences (P ≤ 0.05) in the tenderness of the kilishi samples. For day one, SK3 was more tenderly (7.62 ± 0.38) than the other kilishi samples. For day 50, SK4 had the highest tenderness score of 6.93 ± 0.47compared to others. For days 100 and 150, SK2 had the highest tenderness of 5.80 ± 0.35 and 4.98 ± 0.34 respectively compared to the other kilishi samples. This variation in tenderness of the kilishi samples can be attributed to a large extent on the variations in the ingredients used since the same semitendinosus muscle and processing method were adopted throughout the experiment especially for the sausagetype kilishi samples. Also, this result confirms the report of Moloney [25] who said that meat juiciness is an important component of meat tenderness and palatability. Similarly, the tenderness of the kilishi samples was inversely proportional to the storage duration.
The mean panel ratings for the overall acceptability of the kilishi sample as shown in Tables 3-6 reveals that there were significant (P ≤ 0.05) differences among the kilishi samples. The result obtained in relation to the overall acceptability indicates that the panelist preferred SK2 greatly compared to other kilishi samples in all the storage days. Among the kilishi samples, SK7 had the least rating in overall acceptability. This result obtained indicates that the level of inclusion of the spices used in the kilishi production affected the consumer preference as the panelist preferred SK2 (8.5% ingredients) to the hot pungent SK7 (115% ingredient). This result is in agreement with the findings of Isah and Okubanjo [14].

Conclusion
The present study has demonstrated that inclusion of infusion ingredients to a level of 115% possesses anti-oxidative property that retards oxidative rancidity thus extending the shelf stability of the kilishi. This is justified by the low peroxide, free fatty acid and thiobarbituric acid levels of kilishi sample processed using 115% ingredient inclusion compared to other percentage ingredients inclusion.