Title page for ETD etd-02172006-112041


Document Type Doctoral Thesis
Author Simela, Langelihle
Email langa@nerpo.org.za
URN etd-02172006-112041
Document Title Meat characteristics and acceptability of chevon from South African indigenous goats
Degree PhD (Animal Science)
Department Animal and Wildlife Sciences
Supervisor
Advisor Name Title
Prof M J C Bosman
Prof E C Webb Supervisor
Keywords
  • no key words available
Date 2005-06-13
Availability unrestricted
Abstract
Effects of sex, age and pre-slaughter conditioning on the characteristics of South African indigenous goat carcasses (weight, dimensions, and joint and tissue composition) and quality of chevon (pH and temperature profiles, histological, histochemical, metabolic, proteolytic and physical) were determined. Effects of post-mortem ageing and electrical stimulation on the quality of chevon were also investigated. The nutritional quality of chevon in terms of fatty acid and amino acid content was assessed. The acceptability of chevon compared to mutton was tested by a panel of South African consumers.

The goats were large with live weight, carcass weight and carcass dimensions in the range of the large breeds of southern Africa. They had a high lean and low fat content that is typical of most goat breeds. Intact males were suited for high chevon yield because they were heavy, had a high lean and low fat content, and losses during dressing and chilling were reduced by improved nutrition. Goats between two and six teeth yielded heavy carcasses that were comparable to goats in the eight teeth group, and had proportionately more lean. The hind limb appeared to be ideal for high lean and low fat high value cuts but the dorsal trunk was bony and yielded less lean. Pre-slaughter conditioning improved the overall size of the goats and reduced the losses during slaughter and chilling. It also improved the lean/bone and lean and fat/bone indices.

The M. longissimus thoracis (LT) had a low glycolytic potential (GP), high initial lactate concentration, low initial pH and high ultimate pH (pHu) values, all of which indicated that peri-mortem handling of goats was a potent stressor. Chevon from carcasses with pHu<5.8 had higher initial GP, glycogen and ATP content. It had longer sarcomeres, low 96-hour shear force values and better colour quality than higher pH meat. Similarly, chevon from the 2-teeth group tended to have lower pHu values than contemporary groups and hence lower 96-hour shear force values and better colour quality. Conversely, mature does tended to have high pHu and hence a high mean 96-hour shear force value and a low mean a* value associated with dark cutting meat. Only up to 20% of the muscle samples had a pHu<5.8. Pre-slaughter conditioning had no effect on GP and pHu but enhanced the rate of pH and temperature decline and resulted in more tender meat with higher a* values.

Generally carcasses with a 3-hour pH (pH3) of less than 6.1 were heavier, had more carcass fat, maintained a high temperature early post-mortem, had longer sarcomeres, better colour quality and lower 24-hour shear force values than those with a pH3 of 6.3 or greater. M. longissimus thoracis and M semimembranosus (SM) samples with pH3<6.1 constituted less than 22% of the samples.

The LT and SM had different myofibre proportions. Myofibre types were not useful indices of meat quality. The level of immediate post-slaughter calpastatin activity suggests that the proteolytic potential of chevon is not essentially different from that of other meat types.

Ageing and electrical stimulation improved tenderness and colour quality of chevon. Electrical stimulation increased the rate of pH decline to levels outside the risk of cold shortening as well as the ageing potential of chevon such that the meat attained tenderness that was within the acceptable limits for four days of ageing.

Chevon had high levels of PUFA, particularly C18:2, which were similar to values reported for ostrich. The high C18:2/C18:3 ratio suggested that the n-6/n-3 fatty acid ratio would be much higher than the recommended ratio of less than four. Most of the fatty acid proportions fell within the ranges that have been reported for chevon and other red meat species. Age and sex of the goats had no significant effect on the fatty acid profile but pre-slaughter conditioning resulted in lower levels of C14:0 and total SFA, and increased levels of C18:1 and hence MUFA. The amino acid proportions suggest that there is no variation in the amino acid profile between M. longissimus lumborum muscles from goats of different age or sex classes.

Level of education of the consumers was most important in determining consumer acceptance of the sensory attributes as well as the intended frequency of consumption for chevon and mutton. Population group was a significant factor only when the meats were of more variable acceptability.

Sensory evaluations indicated that chevon and mutton were highly acceptable to the consumers, who were willing to eat any of the meats at least once a week. The study indicated that chevon is acceptable to South African consumers and may be as acceptable as mutton if the meat is from goats of about two years old or younger.

South African indigenous goats may yield high quality chevon, with a low pHu and acceptable colour provided that the meat is from large carcasses (~15kg) with a high fat content (at least 7%) and is not from mature does.

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