Changes in inoculated Escherichia coli O157:H7 populations were determined during drying (62.5 C, 10 h) of whole muscle beef jerky slices pretreated by: (1) immersing in boiling water (94 C, 15 s), then marinating (4 C, 24 h); (2) seasoning (4 C, 24 h), then immersing in a pickling brine (78 C, 90 s); (3) immersing in a vinegar/water (750/750 mL) solution (57.5 C, 20 s), then marinating (4 C, 24 h); and (4) marinating (4 C, 24 h), then immersing in a vinegar/water (750/750 mL) solution (57.5 C, 20 s). Samples were analysed (bacterial enumeration with selective and nonselective agar media, pH, and a w ) following inoculation, each preparation step, and at 0, 4, 6, 8 and 10 h of drying. While all pre-drying treatments resulted in significant ðPo0:05Þ bacterial reductions, treatment 2 resulted in the greatest pre-drying reduction (3.1-4.1 log cfu/cm 2 ) and the highest overall reduction at 10 h drying (5.7-5.8 log cfu/cm 2 ). Total reductions for treatments 1, 3 and 4 after 10 h drying were 4.3-4.5, 4.9-5.2 and 4.7-4.8 log cfu/cm 2 , respectively. Bacterial populations declined to o1.0 log cfu/cm 2 after 30 d storage and remained at this level throughout 90 d storage. These results should be useful in developing guidelines for jerky preparation by consumers and processors.
The effect of a commercial Aspergillus oryzae fermentation extract on the utilization of carbon source and zoospore production by the rumen fungus Neocallimastix frontalis EB 188 was determined. In addition, the composition of a soluble extract prepared from the commercial product was analyzed. This extract was added to N. frontalis EB 188 cultures grown on a variety of substrates and periodically assayed for protein, enzymes, zoospore production, and carbon source utilization. The powdered product contained 93% dry matter, more than 3,000 A. oryzaespores per gram, and did not contain strong buffers or high concentrations of salt. Measurable concentrations of DNA, protein, carbohydrate and several enzymes including cellulase and amylase were also found. Soluble extract increased fungal physiology and treated cultures produced significantly higher levels of supernatant protein and enzymes including amylase, cellulase and beta-glucosidase. The fungal response depended on culture carbon source. However, culture zoospore production was increased regardless of substrate provided. Culture utilization of glucose was more rapid in treated cultures, yet high levels of the extract greatly inhibited glucose utilization.
Beef slices were inoculated (5.7–7.5 log CFU/cm2) with a 4‐strain composite of E. coli O157:H7, stored (4C, 24 h), marinated (4C, 24 h), dried for 10 h at 62.5C or 68.3C, and stored for 90 days at 21C. Unmarinated beef slices dried for 10 h at 62.5C were used to determine the relative contribution of the marinate versus temperature treatment in the 62.5C trials. Samples were analyzed (bacterial enumeration with selective and nonselective agar media, pH, and aw) following inoculation, marinating, at 4, 6, 8 and 10 h of drying, and after 30, 60 and 90 days of storage. Marination resulted in slight changes in bacterial populations (−0.3 to + 0.6 log CFU/cm2), but did not enhance bacterial reduction during drying. For all treatments, most bacterial reductions occurred in the first 4 h of drying, with little reduction thereafter. After 10 h of drying, bacterial reductions were 3.2–3.4 log CFU/cm2 for unmarinated beef slices dried at 62.5C. Reductions of 2.2 and 3.0–4.6 log CFU/cm2 were achieved in marinated jerky slices dried at 62.5C and 68.3C, respectively. No treatment resulted in the recommended 5‐log reduction at the end of 10 h drying. However, bacteria did become undetectable by direct plating (<10 CFU/cm2) following 30 days of storage in all treatments except the unmarinated beef slices plated on tryptic soy agar (TSA). Additional work is needed to develop procedures for adequate destruction of E. coli O157:H7 during drying of beef jerky.
Experiments were performed to determine the effect of Aspergillus oryzae (AO) fermentation extract on zoospore development in the rumen fungus Neocallimastix frontalis EB 188. Powdered product, or liquid extract prepared from such powder, was added at the recommended value for supplementation in dairy cattle. Stationary and stirred cultures were periodically sampled and assayed for extracellular and intracellular protein and enzymes, gas production, zoospore production and maturation, and carbon source utilization. Soluble extract increased fungal physiology when grown in stirred vessels or stationary cultures. Treated cultures produced higher levels of enzymes (nearly double). Mobile zoospores matured into germination entities more rapidly in treated cultures, and when powdered product was used, nearly 3 times more motile zoospores were produced at 56 h of fungal growth. Levels of the intracellular enzyme malate dehydrogenase increased by 6-fold in the presence of powdered product. Product wheat bran carrier used as soluble extract or powder had very little effect on fungal cultures. Medium cellulose was completely hydrolyzed in all cultures but this occurred earlier in those containing AO treatment.
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