20-01-2016, 03:57 PM
This chapter addresses lactic acid fermentation, a process that provides a way to store carcasses for at least 25 weeks and produce an end product that may be both pathogen-free and nutrient-rich. Lactic acid fermentation should be viewed as a means to preserve carcasses until they can be rendered. The low pH prevents undesirable degradation processes. The process of lactic acid fermentation is simple and requires little equipment. Indeed, the process needs only a tank and a grinder. Fermentation is an anaerobic process that can proceed in any sized noncorrosive container provided it is sealed and vented for carbon dioxide release. During this process, carcasses can be decontaminated and there is a possibility of recycling the final products into feedstuff. Fermentation products can be stored until they are transported to a disposal site. Carcasses are ground to fine particles, mixed with a fermentable carbohydrate source and culture innoculant, and then added to a fermentation container. Grinding aids in homogenizing the ingredients. For lactic acid fermentation, lactose,glucose, sucrose, whey, whey permeates, and molasses are all suitable carbohydrate sources.
The carbohydrate source is fermented to lactic acid by Lactobacillus acidophilus. Under optimal conditions, including a fermentation temperature of about 35°C (95°F), the pH of fresh carcasses is reduced to less than 4.5 within 2 days. Fermentation with L. acidophilus destroys many bacteria including Salmonella spp. There may be some microorganisms that can survive lactic acid fermentation, but these can be destroyed by heat treatment through rendering. Biogenic amines produced during putrefaction are present in broiler carcasses. Tamim and Doerr (2000) argue that the presence of a single amine (tyramine) at a concentration above 550 ppm indicates a real risk of toxicity to animals being fed. This concentration is higher in the final product after rendering because the rendered product has less moisture than the fermentation broth. Thus, efforts should be made to reduce putrefaction. Properly prepared products will remain biologically stable until they are accepted for other processes such as rendering.
Taking into account the value of fermentation byproducts, Crews et al. (1995) estimate the cost of fermention of poultry carcasses to be $68-171 per ton. Other calculations that exclude the value of fermentation by-products suggest the costs of fermentation of cattle carcasses to be about $650 per ton. The challenges with lactic acid fermentation are complete pathogen containment, fermentation tank contamination, and corrosion problems. An intriguing idea is to plan for fermentation during the actual transportation of carcasses to the rendering sites; in such a scenario, railroad tank cars could be used for fermentation. This might prove useful, even in the case of an emergency carcass disposal situation. Fermentation could likely be carried out easily in these tank cars, perhaps in less time and with lower costs than other techniques requiring the actual construction of a fermentation tank. Of course, research is needed to ascertain the commercial feasibility of this idea.