No abstract

High-pressure (HP) destruction of Escherichia coli (29055) in apple juice was evaluated (150 to 400 MPa; 0 to 80 min at 25°C) based on a dual destruction behavior consisting of pressure pulse and pressure hold (first order rate) effects. Enumeration was carried out in brain-heart infusion agar (BHIA) and violet-red bile agar (VRBA) to differentiate between surviving cells with and without injury. A pressure pulse at 400 MPa destroyed the entire population (10 8 CFU/mL) of E. coli. During pressure-hold, D values (decimal reduction time) of E. coli decreased with an increase in pressure, and D values from BHIA (survivors including injured cells) were higher than from VRBA (survivors excluding injured cells). Thus, an increasing number of cells were initially injured than killed with HP treatment until finally killed. Pressure dependency of D was described by z-value model with associated z p values (pressure range to result in a decimal change in D values) of 126 and 140 MPa on BHIA and VRBA.

High-moisture ear corn (HMEC) was untreated, treated with propionic acid (PA), or inoculated with a mixture of Lactobacillus plantarum and Enterococcus faecium and allowed to ensile in laboratory silos for 0, 7, 21, 42, 138, or 202 d. The silages were evaluated for fermentation quality, microbial populations, and aerobic stability. In all treatments, silage pH declined rapidly within 7 d, but the rate of decline seemed greatest with the inoculum. The lactic acid content of inoculated HMEC was higher (P < .05) than that of control of PA-treated HMEC. Regardless of treatment, the population of lactic acid bacteria (LAB) increased (P < .1) up to 7 to 21 d of fermentation then declined; LAB counts decreased (P < .05) up to 42 d in control and PA-treated silage but continued to decline until 138 d for inoculated silage. Yeast and mold counts tended to decrease up to 42 d of ensiling then decreased (P < .05) as fermentation progressed. Between 138 and 202 d of ensiling, the control silage showed a marked increase (P < .10) in pH and yeast and mold populations, providing evidence of secondary fermentation; PA treatment and bacterial inoculation prevented secondary fermentation. Inoculation tended to reduce estimates of sample temperature for silage stored for 138 d and exposed to air, but not for the corresponding silage stored for 202 d. Treatment with PA prevented the loss (P > .05) of acetic acid and the rise (P > .05) in pH during air exposure of the 138-d silage; both control and PA-treated silage showed an increase (P < .05) in yeast and mold populations, but the increments were 38% and 23%, respectively. Compared with PA, the relative efficacy of inoculation in improving aerobic spoilage of HMEC depended on the period of silo storage and the criterion used to assess aerobic stability.

No abstract

Attachment of psychrotrophic meat spoilage organisms to longissimus dorsi (1. dorsi) muscle placed in an attachment bath was studied. The numbers of bacteria (log10) attaching to 10.0 g of 1. dorsi muscle during a 20-min incubation period in the attachment bath ranged from 3.88 for Acinetobacter LD-2 to 5.66 for Pseudomonas fluorescens. The lowest attachment values were recorded with two non-motile bacteria, Acinetobacter LD-2 and Moraxella osloensis; the highest, with two motile fluorescent pseudomonads, Pseudomonas putida and P. fluorescens. Attachment strength values (S values) ranged from 0.19 for P. putida to 0.70 for Acinetobacter LD-2. In general, the non-motile bacteria possessed higher S-values than the motile organisms. When two different microorganisms were in contact with the 1. dorsi muscle in the attachment bath, minimal competition for attachment to the meat occurred.