Microflora of minimally processed frozen vegetables sold in Gaborone, Botswana

Two hundred samples of minimally processed, frozen, and prepacked potato chips, peas, corn, and a variety of combined vegetables from supermarkets in Gaborone, Botswana, were examined microbiologically. Determination of aerobic mesophilic plate count, aerobic psychrotrophic plate count, lactic acid bacteria, yeasts and molds, coliforms, Listeria spp., and Staphylococcus aureus were done. Chips had the lowest mean log values for all of the microorganisms enumerated except yeasts and molds. The mean log values for single vegetables ranged from 3.6 to 9.1, 3.4 to 8.9, 2.9 to 5.6, and 2.1 to 6.5 log CFU/ g aerobic mesophilic plate count, aerobic psychrotrophic plate count, lactic acid bacteria, and yeasts and molds, respectively. The microbial profiles of peas and corn were almost similar (P < 0.001). The mean values for combined vegetables were clustered within 4.6 and 5.4 and 4.2 and 5.2 log CFU/g aerobic mesophilic plate count and aerobic psychrotrophic plate count, respectively. All of the vegetables had a coliform population distribution ranging from 0 to < 10(4) most probable number per g. The predominant gram-negative bacteria isolated included members of Enterobacteriaceae and Pseudomonaceae (86.2%). Escherichia coli was not detected in all of the samples. The organisms isolated included those responsible for spoilage in frozen vegetables, namely Pseudomonas, Klebsiella, Corynebacterium, lactic acid bacteria, and Flavobacterium. The predominant lactic acid bacteria were Lactobacillus spp. (55.9%). Other spoilage organisms were yeasts, and Cryptococcus spp. (55.4%) was predominant. Pathogens, namely Listeria monocytogenes, were also isolated at a rate of 2 to 10%, of which 4% was from corn, 2% each from peas and country crop, and 10% from stir-fry. Bacillus cereus was also isolated and accounted for 7.7% of the microorganisms from corn. S. aureus was isolated from all of the vegetables. Enterotoxigenic strains were from corn, peas, mixed vegetables, and stir-fry, and all of them produced enterotoxin A. In addition, the isolates from stir-fry vegetables also produced enterotoxins B and C. The study reveals the presence of pathogens and emerging opportunistic pathogens in the ready-to-use or ready-to-eat vegetables. If E. coli is the only indicator for safety and acceptability, consumers may be exposed to foodborne diseases. Inclusion of other groups as indicator organisms is suggested. Retailers are urged to invest in standby generators to maintain the cold chain.     

Identification and Characterization of Lactic Acid Bacteria Involved in Natural and Lactic Acid Bacterial Fermentations of Pastes of Soybeans and Soybean-Maize Blends Using Culture-Dependent Techniques and Denaturing Gradient Gel Electrophoresis

Pastes of soybeans and soybean-maize blends were fermented with inoculum through back-slopping using lactic acid bacteria (LAB) fermented cereal gruel, thobwa and without inoculum (naturally). LAB involved in the fermentations were characterized using culture-dependent and culture-independent analyses. Decreases in pH from 6.4 to 3.9–4.2 and from 6.9 to 5.4–5.8 after 72 h were observed in LAB fermented pastes (LFP) and in naturally fermented pastes (NFP), respectively. LAB increased from 5.0 to 8.7–9.6 log₁₀ cfu/g in NFP and from 8.1 to 9.3 log₁₀ cfu/g in LFP. LAB in both fermentations were heterofermentative lactobacilli (82.4%) and homofermentative cocci (17.6%), of which 44.7% and 42.9% were exopolysaccharide producers, respectively. Principal component analysis based on carbohydrate fermentation, CO₂ production and arginine hydrolysis showed four clusters dominated by Lactobacillus fermentum, Weissella confusa, Lactobacillus brevis 1 and Pediococcus pentosaceus, respectively. Sequencing of 16S rDNA gene confirmed Lb. fermentum, W. confusa/W. cibaria, and P. pentosaceus as identities of species in three clusters. Denaturing gradient gel electrophoresis (DGGE) confirmed these species as the dominant microbiota. DGGE showed higher similarity in microbial profiles of LFP throughout fermentation and low similarity in NFP during early and late stages of fermentation.     

Route optimization using the distributed binding update for nested mobile networks

Although many researches on network mobility management have been carried out, a binding update storm, signaling overheads, and so on still exist in the past proposals. To avoid the binding update storm and to support route optimization as well as intra‐domain data communication, a specifically designed solution with a distributed manner is proposed in this paper. By applying the derived analytical results, we demonstrate that the proposed solution is able to significantly outperform the closely related work in the literature.Copyright © 2012 John Wiley & Sons, Ltd.