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Food Structure

Abstract

Ultrastructural changes in meat incubated with different concentrations of acetic acid were investigated by transmission electron microscopy. Discs of bovine M. longissimus dorsi (48 h postmortem) were incubated at 46 C for 48 h in various acetlc acid solutions, giving discs with pH values ranging from 5.1 to 3.9 . Below pH 4. 5 , the volume of the discs increased markedly due to water absorption.

Discs incubated in 0.01M acetic acid had a pH of 5.1, lower swelling ratios and shorter sarcomeres than control samples at pH 5. 5. Structural studies of the samples at pH 5.1 revealed that A-band length decreased whereas I-band length increased . There was fragmentation of thin filaments in the Z-line region and disorganization of Z-line structure.

In discs treated with O.O5M acetic acid (meat pH 4.5), complete loss of M-lines was observed. Noticeable swelling also occurred across the muscle fibre axis , mainly in the A-band region, and myosin filaments were partially extracted. Z-lines were swollen, disorganized and slightly fragmented.

Below pH 4. 5 , swelling became much more pronounced with further extraction of myosin filaments. Most of the actin filaments were extracted and myofibrils fused together giving an amorphous, coagulated appearance. Z-lines were partially extracted.

In general, the greatest amount of swelling occurred across the muscle fibre axis although significant in creases in sarcomere length were observed at pH 4.5 and below.

Cooking of control and O.01M acid treated meat discs at 80°C increased the space between myofibrils whereas minimal shrinkage was not iced in samples below pH 4.5.

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