Alicyclobacillus spoilage and control - a review.

In the last few decades Gram positive non pathogenic, rod shaped, thermo-acidophilic and acid-tolerant spore-forming bacteria such as Alicyclobacillus spp. have been identified as the causative agent in spoilage of commercially pasteurized fruit juice. In particular, A. acidoterrestris is considered a major producer of off-flavors. The spores of A. acidoterrestris possess the ability to survive commercial pasteurization processes, to germinate and grow in low pH environments and to produce volatile, unpleasant odorous compound (guaiacol) in fruit juices. The flat sour type of spoilage (without gas production or package swelling) is characterized as having a "medicinal," "smoky," and "antiseptic" off-flavor and makes the final juice product unacceptable. Spoilage by Alicyclobacillus is a major concern for producers since many of the new methods, which can destroy spores in the absence of chemical additives, may not destroy Alicyclobacillus. Although A. acidoterrestris is not pathogenic to humans, it can result in significant economic losses to juice processors because of its odor. The present review includes the taxonomy of Alicyclobacillus spp., their general characteristics, their resistance to heat and possible off-flavor production pathways. Particular emphasis is given to commonly used control measures, including physical, chemical and biological treatments currently available for removal of Alicyclobacillus spp.

Lactic acid bacterial population dynamics during fermentation and storage of Thai fermented sausage according to restriction fragment length polymorphism analysis.

This study applied restriction fragment length polymorphism (RFLP) analysis to identify the lactic acid bacteria (LAB) isolated from "mum" Thai fermented sausages during fermentation and storage. A total of 630 lactic acid bacteria were isolated from the sausages prepared using 2 methods. In Method 1, after stuffing, the sausages were stored at 30 °C for 14 days. In Method 2, after stuffing and storage at 30 °C for 3 days, the sausages were vacuum-packed and stored at 4 °C until Day 28. The sausages were sampled on Days 0, 3, 14, and 28 for analyses. The 16S rDNA was amplified and digested using restriction enzymes. Of the restriction enzymes evaluated, Dde I displayed the highest discrimination capacity. The LAB were classified and 7 species were identified For Methods 1 and 2, during fermentation, the Lactobacillus sakei and Lactobacillus plantarum species were dominant. For Method 2, the proportion of Leuconostoc mesenteroides markedly increased during storage, until L. sakei and Ln. mesenteroides represented the dominant species. The identification of LAB in the sausage samples could facilitate the selection of appropriate microorganisms for candidate starter cultures for future controlled mum production.

Pyrone polyketides synthesized by a type III polyketide synthase from Drosophyllum lusitanicum.

To isolate cDNAs involved in the biosynthesis of acetate-derived naphthoquinones in Drosophyllum lusitanicum, an expressed sequence tag analysis was performed. RNA from callus cultures was used to create a cDNA library from which 2004 expressed sequence tags were generated. One cDNA with similarity to known type III polyketide synthases was isolated as full-length sequence and termed DluHKS. The translated polypeptide sequence of DluHKS showed 51-67% identity with other plant type III PKSs. Recombinant DluHKS expressed in Escherichia coli accepted acetyl-coenzyme A (CoA) as starter and carried out sequential decarboxylative condensations with malonyl-CoA yielding alpha-pyrones from three to six acetate units. However, naphthalenes, the expected products, were not isolated. Since the main compound produced by DluHKS is a hexaketide alpha-pyrone, and the naphthoquinones in D. lusitanicum are composed of six acetate units, we propose that the enzyme provides the backbone of these secondary metabolites. An involvement of accessory proteins in this biosynthetic pathway is discussed.

A polyketide synthase of Plumbago indica that catalyzes the formation of hexaketide pyrones.

Plumbago indica L. contains naphthoquinones that are derived from six acetate units. To characterize the enzyme catalyzing the first step in the biosynthesis of these metabolites, a cDNA encoding a type III polyketide synthase (PKS) was isolated from roots of P. indica. The translated polypeptide shared 47-60% identical residues with PKSs from other plant species. Recombinant P. indica PKS expressed in Escherichia coli accepted acetyl-CoA as starter and carried out five decarboxylative condensations with malonyl coenzyme A (-CoA). The resulting hexaketide was not folded into a naphthalene derivative. Instead, an alpha-pyrone, 6-(2',4'-dihydroxy-6'-methylphenyl)-4-hydroxy-2-pyrone, was produced. In addition, formation of alpha-pyrones with linear keto side chains derived from three to six acetate units was observed. As phenylpyrones could not be detected in P. indica roots, we propose that the novel PKS is involved in the biosynthesis of naphthoquinones, and additional cofactors are probably required for the biosynthesis of these secondary metabolites in vivo.