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Profiling of traditional South African biltong in terms of processing, physicochemical properties and microbial stability during storage

Jones M.. 2017. Stellenbosch : Stellenbosch University, 128 p.. Thesis Ph. D. -- Food science.

In South Africa, there are no processing guidelines for biltong production and therefore the industry uses different processing parameters which results in variation in the product. The same process was used throughout this study and drying was done using constant parameters ¿ temperature 25 ± 2°C, relative humidity 30 ± 5%, air velocity 2 ± 0.2 m/s. An initial study investigating the influence of vinegar addition during the production of beef biltong showed that vinegar addition does not influence its drying kinetics. The biltong reached a 50% weight loss after 66 hours and a 65% weight loss after 96 hours. The use of different meat muscles (topside, semimembranosus and silverside, biceps femoris), beef with subcutaneous fat and gemsbok (Oryx gazelle) showed differences (p = 0.05) in drying rates when dried to a targeted weight loss of 65%. The two lean beef muscles both dried in 96 hours. The gemsbok topside took only 78 hours with a drying pattern similar to the lean beef topside. The fatty beef topside took 118 hours to dry. The microbiological profile of beef biltong over a three month shelf-life storage were studied. Final weight loss during drying and packaging method (modified atmospheric packaging and vacuum packaging) did not have an effect (p > 0.05) on the microbiological profile. Total viable counts and coliforms were only reduced in biltong with vinegar added. After drying, yeasts and moulds were already present at high levels (~ 2.5 log cfu.g-1) but not visible. After six weeks, yeasts and moulds became visible. Staphylococcus aureus was present at less than 20 log cfu.g-1 while Listeria monocytogenes, Salmonella spp. and Escherichia coli were not present during the three month storage period. Yeast and mould growth on biltong is a problem and therefore a challenge study was included. Beef biltong produced without and with vinegar and dried to a 50% or 65% weight loss were inoculated with yeasts and moulds. No yeast and mould growth was seen on biltong with vinegar but 1.8 ¿ 2.5 log cfu.g-1 was detected after 34 days. Biltong without vinegar showed yeast and mould growth after 10 days with levels of 2.8 ¿ 3.1 log cfu.g-1. Saccharomyces spp. (yeast) and Aspergillus spp., Fusarium spp. and Penicillium spp. (moulds) were the most common yeast and moulds. A small-scale study using ultrasound in the salting step of beef biltong processing showed that ultrasonic-brining did not have an effect on either the salting or drying kinetics contrary to what was expected. Throughout the study the physicochemical properties of the beef biltong gave consistent results. An approximate 50% and 65% weight loss produced biltong with a moisture content of 50% and 30%, respectively and water activity of 0.74 ¿ 0.78 and 0.81 and 0.86, respectively. Weight loss or the addition of vinegar did not play a role in the salt content (dry basis). Beef biltong without vinegar had a pH 5.56 ¿ 5.75 while the addition of vinegar to biltong lowered the pH of biltong to 4.89 ¿ 4.93. It is recommended that the biltong industry should standardise their drying parameters to avoid variation in quality and for a more microbial stable product. Vinegar could be added as it has an effect on the yeast and mould growth. Biltong with water activity ranging from 0.74 to 0.83 does not have a shelf-life of more than three months when using modified atmosphere packaging or vacuum packaging. The data generated in this study serves as a base-line for future studies focused on optimising and standardising the drying procedures applicable to biltong....

Mots-clés : viande séchée; stockage des aliments; propriété physicochimique; aptitude à la conservation; traitement des aliments; afrique du sud; biltong; alimentation traditionnelle

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