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Research & Development

Microbiology of Chinese Xuanwei ham production
By Aixiang Huang, Sarote Sirisansaneeyakul, Zongdao Chen, Shouchun Liu and Yusuf Chisti

Keywords
t Chinese Xuanwei ham t Dry-cured ham tMicroflora t Proteases t Lipases

Xuanwei ham of China is a popular dry-cured meat, but microbiology of its production is barely known. Surface microfloral changes accompanying production of Xuanwei ham are reported. Fifty hind legs of pigs were processed to dry-cured ham using an approximately 190 days long traditional process that involved salting, drying and fermentation as the major steps. Surfacecounts of microorganisms declined to low levels within 28 days as a consequence of salting. During the subsequent drying stage, microbial counts generally peaked within the first 40 days and subsequently declined progressively. Peak microbial counts were 4.7x108 cfu/cm2 on the ham surface.

Yeasts never became predominant. Moulds were dominant during the fermentation stage on the surface of theham. A majority (>89%) of the bacterial isolates were staphylococci. Proteolytic and lipolytic activities were identified in many of the isolated bacteria and yeasts. Surface microorganisms involved in production of Xuanwei ham appear to be mainly staphylococci and species of Penicillium and Aspergillus. Yeasts appear to contribute, but to a lesser extent than bacteria and moulds. Understandingthe progression of microbial changes during ham processing should allow production of ham batches of a consistent quality.

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uanwei ham is a famed uncooked dry-cured ham of China. The ham is produced in Xuanwei, a city in the Yunnan Province, southwestern China. Xuanwei ham is characterised by its rosered colour and a unique flavour. Nearly 20,750 t of Xuanwei ham are produced annually. Thetraditional production process uses hind legs of a local breed of pig. Cut and trimmed legs (i.e. ‘green ham’) that have been pressed by hand to remove blood are held under cool conditions for 24 h for ripening the meat. The legs are then salted by hand. This is followed by a 40-day drying stage and then by a 120day fermentation stage. The total process takes nearly 190 days. Figure 1 illustratesthe main stages of production of Xuanwei ham. Although Xuanwei ham has been produced since the Qing Dynasty (1727 AD) (YU et al., 2005), the chemical, physical and microbiological changes accompanying its production are only now being understood. Some of the quality attributes of Xuanwei ham have been linked to certain yeasts (JIANG et al., 1990), bacteria such as micrococci and staphylococci, andmoulds that occur in the final product (LI et al., 2003). The information about the microbiology of Xuanwei ham is sometimes contradictory. For example, according to some sources (JIANG et al., 1990; WANG et al., 2006), moulds do not play a direct role in determining the quality of Xuanwei ham, but traditional producers and many consumers hold that high quality Xuanwei ham must have a ‘green coat’of moulds on it. Similarly, moulds are believed to be essential contributors to flavour development in some European dry-cured hams (LÜCKE, 1986; MARTÍN et al., 2004). The beneficial role of moulds notwithstanding, some moulds certainly produce mycotoxins in Xuanwei and other dry-cured hams (WANG et al., 2006; ROJAS et al., 1991; NÚÑEZ et al., 1996a). This work reports on changes in the surfacemicroflora and the pH, water activity, and salt content of the meat during production of Xuanwei ham. Endogenous and microbial enzymes such as lipases and proteases are known to contribute to flavour development in many dry-cured hams (TOLDRA, 1998). Therefore, the proteolytic and lipolytic activities of some of the microorganisms isolated from ham were assessed and are reported. Microbiology of...
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