ABSTRACT
This study was carried out to investigate the effect of different marinades on quality characteristics of chevon jerky. Chevon (Hindquarter muscle) was treated with marinades containing different levels of vinegar (0, 2.5% or 5% v/v) and papain (0, 0.004g/0.04gw/v). A 3×3 factorial design which composed of nine treatments with three replicates was used. Chevon was cut into 1.5cm x 1.5cm cubes and samples were marinated for 12h and dried in an oven for 10h at temperature of 65oC. Sensory and microbial characteristics, drying rate and rehydration ratio were determined. The samples for sensory analysis were vacuum packaged after drying and stored at room temperature. Due to the risk of mould growth on samples from treatments containing papain only (T2 and T3) after 15d of storage in a preliminary work, sensory evaluation was conducted on samples stored for 1d and 15d. Panelists were presented with randomly coded cooked samples and the tenderness, chewiness, juiciness; flavour and overall liking of the samples were evaluated using 8 point hedonic scale. The result of sensory properties showed that out of the nine treatments tested, papain (0.04g) was effective in tenderising the chevon jerky compared with all the other treatments. Samples were ranked as very tender to extremely tender while samples treated with vinegar (5%) was ranked as moderately tough to slightly tough. Samples from control (T1) obtained the highest acceptability score of 52.78% and was ranked as ―very like to extremely like‖ whereas papain 0.004g +vinegar 2.5% (T5) was the least scored 38.88% and was ranked as ―slightly like to moderately like‖. No significant (p > 0.05) differences were observed among treatments for chewiness, juiciness and flavour. However, juiciness improved with longer storage time at 15d. Samples evaluated at 1d were rated as ―extremely dry to very dry‖ (24.69%) but were ranked as ―very juicy to extremely juicy‖ (24.08%) at 15d. Samples for microbial test
were also vacuum packaged and stored at room temperature. Additionally, microbial quality analysis was conducted at 1d, 15d and 30d of storage and the effects of the nine treatments on the growth of four different microbes (total plate count, Staphylococcus aureus, E.coli, yeast and mould) during storage were investigated. As storage period increased from 15 to 30d total plate count increased from1.59 to 1.93log cfu/g, while E.coli count declined from 0.19 to 0.09log cfu/g. Additionally, Staphylococcus count decreased from 1.96 to 0.00log cfu/g and lastly as storage period progressed from 15d to 30d yeast and mould count declined from 1.17 to 0.30log cfu/g. Drying rate was determined by change in % moisture content per unit time during drying for 10h. The analysis showed that all the test samples recorded lower moisture content compared to that of the control (T1) after drying. Samples from vinegar (2.5%) recorded the least (1.71%) moisture content whereas the highest (3.61%) was observed in control (T1) samples. Rehydration studies were carried out on sample (1.5cm x 1.5cm) to distilled water ratio of 1:40 for 300min under ambient condition. As rehydration time progressed from time 0 to 300min there was an increase in weight among all test samples. Samples from control (T1) recorded the least moisture uptake of 9.83 whereas samples from vinegar 2.5% (T4) recorded the highest moisture uptake (19.94) after rehydration. Overall, the results of this study indicate that although overall likeness score favoured the control treatment, it is possible to improve meat toughness using papain to produce meat with acceptable sensory attribute than vinegar. Also, the drying process resulted in a jerky product with low moisture content which inhibited microbial growth; however, vinegar can be used in jerky production to add flavour to the product.
CHAPTER ONE
Introduction
Meat is an excellent source of many important nutrients; however, it is subject to high rate of deterioration. It is also an ideal environment for bacterial to thrive due to its high protein and moisture contents (Bhaisare et al., 2014). Microbial deterioration of meat begins soon after exsanguinations. The quantity of spoilage microorganism present in fresh meat at the time of processing has an impact on product‘s shelf life. Bacteria, mould and yeast are the three common microorganisms found in meat. The moulds and yeast growing on meat are aerobic whereas bacteria thriving in meat could be aerobic, anaerobic or facultative (Jay et la., 2008). Some additional organisms of concern affiliated with meat in general are Salmonella, Escherichia coli, Staphylococcus aureus etc (Romans et al., 1994).Therefore, meat processing methods such as refrigeration, canning and drying aim at limiting microbial growth at the least, making it possible to extend shelf life and also introduces variety of meat products. The process of freezing may decrease the number of microorganisms during storage. However, some species of bacteria found during refrigerated storage such as Pseudomonas, Brochothrix thermosphacta and lactic acid bacteria (LAB) (Lactobacillus, Carnobacterium, and Leuconosto) etc can survive this process and resume growth (Labadie, 1999; Ellis and Goodacre, 2001; Pin, et al., 2002). On the other hand most traditional products have relied on salting and drying as a means of meat preservation.
Jerky is a form of processed meat in which fresh meat is dried to prevent it from early deterioration. The meat may be cut into smaller pieces or minced and then mould into strips or put into narrow casings (Nummer et al., 2004). Salt, spices or marinades are
used to inhibit microbial growth and to flavour the meat (USDA – FSIS, 2004). Jerky can be processed from basically any defatted meat such as beef, chicken, pork (Calicioglu et al., 2003; Pegg et al., 2006; Han et al., 2007) and chevon.
Quality characteristics of meat products deteriorate due to microbial growth and rancidity of lipids in the course of storage (Aguirrezabal et al., 2000). The intent of processing and preservation is to mitigate such processes to extend the shelf life of processed meat products. To attain stability, jerky is dehydrated to water activity 0.70 to 0.85 (Quintion et al., 1997), without the need for refrigeration due to the control of the growth of bacteria at low water activity. However, despite the imposition of this hurdle (low water activity) in jerky manufacturing, the connection of jerky products with food borne disease outbreaks (CDC, 1995; Eidson et al., 2000) has raised questions about their safety. In order to address this challenge, vinegar can be used to effectively control pathogens in jerky products (Calicioglu et al., 2002a). Acetic acid (vinegar) is usually used in the meat manufacturing sectors as an organic chemical to decontaminate meat (Ricke, 2003). Acetic acid exerts its action based primarily on its acidifying influence. It manifests this acidifying action only in an undissociated form (Sofos et al., 1998). Acetic acid efficacy in arresting development or destroying food pathogenic bacteria could differ among treatments based on the percentage of undissociated acid at a given pH. Generally, all products treated with organic acids could restrict microbes‘ development or existence; however the degree of their existence is based on the types of organism harboured in the meat and the kind and quantity of organic acid, especially its buffering capacity.
Whole muscle jerky is tough due to the low moisture content to prevent microbial growth. Some restructured jerky products have a tender texture yet high in fat and water activity, which induced lipid rancidity and microbial growth (Quinton et al., 1997). On the other hand, whole muscle jerky can also be reconstituted in water to soften it; however, it is time consuming. According to Huffman et al. (1996) a very tender meat is considered as the most essential eating property by consumers. Researchers have shown that meat tenderness is chiefly linked with the structural firmness of myofibrillar and connective tissue proteins (Marsh and Leet, 1966; Nishimura et al., 1995). Several methods, including mechanical tenderisation, elevated-temperature storage, calcium chloride injection, electrical stimulation, organic acids treatments and enzymatic tenderisation, have also been used to enhance meat tenderness (Moeller et al., 1976; Savell et al., 1981; Koohmaraie et al., 1988; Koohmaraie, 1992; Hwang et al., 2000). Jerky toughness can be altered by the application of enzymatic tenderisers such as papain and bromelain. Papain is an enzymatic protease with very broad specificities and degrades connective tissue and myofibrillar proteins, sometimes leading to excessive tenderisation and distortion of sensory attribute (texture) of product (Miller et al., 1989). Chen et al. (2006) reported that papain tenderise meat within a short time and is superior because of safety issues such as pathogenicity, compared to the other procedures of meat tenderisation. Similarly, bromelain is an enzymatic protease that exists naturally in pineapple plant and has been applied broadly as a meat tenderiser (Omojasola et al., 2008). However, Sullivan and Calkins (2010); Rawdkuen and Benjakul (2012) reported that papain is most effective in improving meat tenderness than bromelain. The two most often used enzymes in marinades are papain and bromelain.
A marinade is a sauce which is designed to flavour and tenderise meats. Additionally, they improve meat juiciness and also enhance protection and shelf life of processed meat products through inhibition of microbial development (Alvarado and McKee, 2007). The efficacy of most marinades is based on the ingredients that are used (organic acids, soy sauce, essential oils, salts, tenderisers and spices). Therefore, there is the need to explore the benefits of marinades to enhance meat quality. The Government of Ghana‘s policy is to increase small ruminant production and has supported 90 farmers in the Central, Western and Eastern regions with superior breeds of 650 sheep and 450 goats under the West Africa Agricultural Productivity Programme (WAAPP) (Ablordeppey and Osabutey, 2015). There is the possibility of a potential increase in chevon production and value addition will be required to improve marketability of the raw meat, therefore the need to introduce jerky as a form of meat preservation.
Problem Statement
Most animals slaughtered in Ghana for meat consumption are over aged and meat tenderness decreases as animals increase in age. The decreased tenderness is due to increase in collagen cross-linking which is regarded as the chief determinants of meat texture. Meat from over aged animals require longer cooking time for it to tenderise, chewing such meat is also difficult and it will as well require a longer digesting time. Since jerky is dried to a low water activity in order to inhibit microbial growth, one might anticipate that using whole muscle from over aged animals would result in very tough and coarse textured jerky. Additionally, despite the low water activity there have been several reports on the outbreak of food borne diseases connected with the consumption of snack meat products (CDC, 1995; Eidson et al., 2000). Hence, this
has raised questions about their safety, since jerky is consumed without further cooking. There is a dearth of knowledge in the use and effect of acidic and enzymatic marinades in the meat processing industry.
Objectives
The general objective of this study is:
To evaluate the effect of acidic (vinegar) and enzymatic (papain) marinades on quality characteristics of chevon jerky (produced by oven drying).
The specific objectives are:
- Evaluate the effect of the marinades on sensory characteristic of chevon jerky.
- Compare the effect of the treatments on microbial characteristics and shelf life of chevon jerky during storage.
