Clostridium perfringens food poisoning is caused by type A isolates carrying a chromosomal enterotoxin (cpe) gene (C-cpe), while C. perfringens-associated non-food-borne gastrointestinal (GI) diseases are caused by isolates carrying a plasmid-borne cpe gene (P-cpe). C. perfringens spores are thought to be the important infectious cell morphotype, and after inoculation into a suitable host, these spores must germinate and return to active growth to cause GI disease. We have found differences in the germination of spores of C-cpe and P-cpe isolates in that (i) while a mixture of L-asparagine and KCl was a good germinant for spores of C-cpe and P-cpe isolates, KCl and, to a lesser extent, L-asparagine triggered spore germination in C-cpe isolates only; and (ii) L-alanine or L-valine induced significant germination of spores of P-cpe but not C-cpe isolates. Spores of a gerK mutant of a C-cpe isolate in which two of the proteins of a spore nutrient germinant receptor were absent germinated slower than wild-type spores with KCl, did not germinate with L-asparagine, and germinated poorly compared to wild-type spores with the nonnutrient germinants dodecylamine and a 1:1 chelate of Ca 2؉ and dipicolinic acid. In contrast, spores of a gerAA mutant of a C-cpe isolate that lacked another component of a nutrient germinant receptor germinated at the same rate as that of wild-type spores with high concentrations of KCl, although they germinated slightly slower with a lower KCl concentration, suggesting an auxiliary role for GerAA in C. perfringens spore germination. In sum, this study identified nutrient germinants for spores of both C-cpe and P-cpe isolates of C. perfringens and provided evidence that proteins encoded by the gerK operon are required for both nutrient-induced and non-nutrient-induced spore germination.Bacillus and Clostridium species have the ability to form metabolically dormant spores that are extremely resistant to environmental stresses, such as heat, radiation, and toxic chemicals (41, 50). As a consequence of this resistance, spores of a number of these species are significant agents of food spoilage and food-borne gastrointestinal (GI) diseases (51). However, to cause deleterious effects, dormant spores must first go through germination and then outgrowth to be converted to vegetative cells. Spore germination has been studied most extensively for Bacillus subtilis (31,40,49) and can be initiated by a variety of chemicals, including nutrients, cationic surfactants, and enzymes, as well as by hydrostatic pressure (37). Nutrient germinants for spores of Bacillus species include L-alanine, a mixture of L-asparagine, D-glucose, D-fructose, and potassium ions (AGFK), and inosine (8, 32, 49). These nutrient germinants interact with cognate receptors located in the inner spore membrane (20, 36), stimulating the release of monovalent cations (H ϩ , Na ϩ , and K ϩ ), divalent cations (Ca 2ϩ , Mg 2ϩ , and Mn 2ϩ ), and the spore core's large depot (ϳ20% of core dry weight) of pyridine-2,6-dicarboxylic acid (dipico...

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Many volatile compounds generated during the thermal processing of milk have been associated with cooked, stale, and sulfurous notes in milk and are considered as off-flavor by most consumers. A headspace solid-phase microextraction (HS-SPME)/gas chromatographic technique for the quantitative analysis of thermally derived off-flavor compounds was developed in this study. The extraction temperature, time, and sample amount were optimized using a randomized 2(3) central composite rotatable design with 2 central replicates and 2 replicates in each factorial point along with response surface methodology. Calibration curves were constructed in milk using the standard addition technique, and then used to quantify 20 off-flavor compounds in raw, pasteurized, and UHT milk samples with various fat contents. The concentrations of these volatiles in raw and pasteurized milk samples were not significantly different. However, dimethyl sulfide, 2-hexanone, 2-heptanone, 2-nonanone, 2-undecanone, 2-methylpropanal, 3-methylbutanal, heptanal, and decanal were found at higher concentrations in UHT milk as compared with raw and pasteurized milk samples. In addition, the concentration of methyl ketones was greater in UHT milk with higher fat content. The calculated odor activity values suggested that 2,3-butanedione, 2-heptanone, 2-nonanone, 2-methylpropanal, 3-methylbutanal, nonanal, decanal, and dimethyl sulfide could be important contributors to the off-flavor of UHT milk. The HS-SPME technique developed in this study is accurate and relatively simple, and can be used for the quantification of thermally derived off-flavor compounds in milk.

Volatile sulfur compounds have been reported to be responsible for the sulfurous off-flavors generated during the thermal processing of milk; however, their analysis has been a challenge due to their high reactivity, high volatility, and low sensory threshold. In this study, reactive thiols were stabilized and the volatile sulfur compounds in milk were extracted by headspace solid-phase microextraction, and analyzed by gas chromatography and pulsed-flame photometric detection. Calibration curves for 7 sulfur-containing compounds were constructed in milk by the standard addition technique. Raw, pasteurized, and UHT milk samples with various fat contents were analyzed. Compared with raw and pasteurized samples, UHT milk contained substantially higher concentrations of hydrogen sulfide, methanethiol, carbon disulfide, dimethyl trisulfide, and di-methyl sulfoxide. The high odor activity values calculated for methanethiol and dimethyl trisulfide suggested that these 2 compounds, in addition to di-methyl sulfide reported in a previous study, could be the most important contributors to the sulfurous note in UHT milk.

The food-processing industry has made large investments in processing facilities relying mostly on conventional thermal processing technologies with well-established reliability and efficacy. Replacing them with one of the novel alternatives recently developed is a decision that must be carefully approached. Among them, high-pressure processing (HPP), at room or refrigerated temperature, is now a wellestablished option experiencing worldwide commercial growth. Surveys have shown an excellent consumer acceptance of HPP technology. For financial feasibility reasons, HPP treatments must be kept short, a challenge that can be met by some of the alternatives here reviewed such as the use of the hurdle technology concept. Although HPP technology is limited to pasteurization treatments, the combination of high pressure and high temperature used in pressureassisted thermal processing (PATP) can be used to sterilize foods. An analysis of alternatives to achieve the inactivation of bacterial spores at the lowest temperature possible highlights the need for additional research on the use of germinants. Because of incomplete research, PATP presents several implementation challenges, including the modeling of food temperature, the determination of inactivation kinetics particularly for bacterial spores, and the prediction of chemical changes including the potential formation of toxic compounds.