Pongphen Jitareerat

Effect of chitosan on ripening, enzymatic activity, and disease development in mango (mangifera indica) fruit

Abstract The effects of chitosan on mycelial growth and spore germination of Colletotrichum gloeosporioides were investigated on potato dextrose agar (PDA) containing 0%, 0.5%, 1.0%, 1.5%, and 2.0% (w/v) chitosan dissolved in 0.5% acetic acid. Complete inhibition of mycelial growth and spore germination was observed in the medium containing only 0.5% acetic acid. Media containing chitosan were less inhibitory, but the highest concentrations of chitosan, at 1.5% and 2.0%, were more inhibitory than the lower concentrations (0.5% and 1.0%). Chitosan treatment (0.5%, 1.0%, 1.5%, and 2.0%) of mangoes {Mangifera indica) previously inoculated with C. gloeosporioides resulted in a lower rate of disease progression compared with the controls. Chitosan concentrations of 0.5% and 1.0% had stimulatory effects on chitinase and P‐l,3‐glucanase activities. Additionally, chitosan coatings in mangoes delayed ripening and reduced respiration rate, ethylene production, and the loss of weight, ascorbic acid, and total titratable acidity. However, the firmness of mangoes treated at concentrations above 1% caused a perceptible decline in sensory quality.

Fates of seeded Escherichia coli O157:H7 and Salmonella on selected fresh culinary herbs during refrigerated storage.

The fates of seeded Escherichia coli O157:H7 and Salmonella on selected fresh culinary herbs were evaluated at a refrigerated temperature (4 degrees C). Fresh herbs, including cilantro, oregano, basil, chive, parsley, and rosemary, were inoculated with six-strain mixtures of E. coli O157:H7 and Salmonella, and the microbial populations were monitored at 1, 5, 11, 16, 19, and 24 days. For both pathogens, a significant decrease in the population (P < 0.0001) occurred within the first 5 days of storage (< 0.8 log). Both pathogens remained the highest on cilantro and the lowest on rosemary (P < 0.0001). Storage time had a significant effect on the survival of E. coli O157:H7; populations declined as storage time progressed. Although storage of cilantro, basil, and chive was terminated after 19 days because of deteriorated quality, significant numbers of both pathogens were recovered from the remaining fresh herbs after 24 days of storage. The results showed that both bacteria were extremely persistent on all test herbs under the test conditions. The results also reinforce the concept that, once contaminated, bacterial pathogens can persist on fresh herbs throughout a normal distribution time.

Low-Dose Irradiation Improves Microbial Quality and Shelf Life of Fresh Mint (Mentha piperita L.) without Compromising Visual Quality

UNLABELLED The effects of low-dose irradiation (0.25 to 2 kGy) and postirradiation storage (at 4 degrees C) on microbial and visual quality, color values (L*, a*, b*, chroma, and hue [ degrees ]), and chlorophyll content (Chl a, Chl b, and total Chl) of fresh mint were evaluated. Samples inoculated with E. coli O157:H7, Salmonella, and MS2 bacteriophage were irradiated and evaluated. E. coli O157:H7 and Salmonella populations were reduced by 2 to 2.4, 3.5, and 5.8 log CFU/g, respectively, 1 d after treatment with 0.25, 0.60, and 1 kGy, respectively, and were completely eliminated at 2 kGy. None of the irradiation doses (P < 0.0001) reduced MS2 bacteriophage populations by more than 0.60 log PFU/g. Irradiation doses did not affect visual quality and samples remained of excellent to good quality (score 7.75 to 9) for up to 9 d of storage. Irradiation at 0.60, 1, and 2 kGy increased (P < 0.0001) Chl a, Chl b, and total Chl. Both total Chl and Chl a decreased significantly after 3 d of storage. Significant decreases in Chl b were not observed until day 12 of storage. Color values (L*, b*, and chroma) were not significantly different until day 6 of storage and hue ( degrees ) remained unchanged (179 degrees ) for the entire storage period of 12 d. Overall, irradiation did not change L*, a*, b*, or chroma. These results demonstrate that irradiation of fresh mint at 2 kGy has the potential to improve its microbial quality and extend its shelf life without compromising its visual quality and color. PRACTICAL APPLICATION Mints and other raw fresh herbs are widely used for flavoring as well as garnish in a variety of dishes without further cooking. However, mint is one considered as one of the high-risk herbs when it comes to microbial contamination. We have evaluated the use of gamma irradiation treatment at very low doses ranging from 0 to 2 kGy to eliminate seeded Salmonella spp, E. coli O157:H7, and MS2 bacteriophage, a surrogate of hepatitis A virus. We found that low-dose irradiation (1.0 to 2.0 kGy) appears to be a promising method for improving the microbiological quality of fresh mint without compromising its visual and color attributes. This method may be applied to many popular fresh culinary herbs that are commonly used as garnishes in Asian cuisine.

Comparative study of regulatory mechanisms for pectinase production by Erwinia carotovora subsp. carotovora and Erwinia chrysanthemi.

The production of pectinase, the major virulence determinant of soft-rot Erwinia species, is controlled by many regulatory factors. We focused on the major regulatory proteins, KdgR, CRP, Pir, and PecS, characterized mainly in E. chrysanthemi, and tested for their presence and function in the control of pectate lyase (Pel) and polygalacturonase (Peh) production in E. carotovora subsp. carotovora. Homologues of kdgR and crp but not of pir and pecS were detected by Southern blot analyses in E. carotovora subsp. carotovora. In fact, KdgR and CRP homologues of E. carotovora subsp. carotovora had high amino acid identities to those of E. chrysanthemi, including a complete match of the hypothetical helix-turn-helix DNA-binding motif. However, in Western blot analyses using anti-Pir (E. chrysanthemi) antibodies, a cross-reacting protein was present in both Erwinia species, although Pel production in E. carotovora subsp. carotovora was not further stimulated by adding plant extract into the medium containing PGA (polygalacturonic acid) in which hyperinduction by Pir has been reported in E. chrysanthemi EC16. When plasmids that contained each of these regulatory genes from E. chrysanthemi were introduced into E. carotovora subsp. carotovora, Pel production was controlled as predicted from their roles in E. chrysanthemi, except for PecS. PecS exerted a positive control in E. carotovora subsp. carotovora, in contrast to a negative control in E. chrysanthemi. DNA-binding assays demonstrated that KdgR, CRP, Pir, and PecS of E. chrysanthemi and KdgR and CRP homologues of E. carotovora subsp. carotovora could bind to the promoter regions of pel-1, pel-3, and peh of E. carotovora subsp. carotovora. Taken together, KdgR and CRP homologues of E. carotovora subsp. carotovora may regulate Pel and Peh production as in E. chrysanthemi. However, the presence of Pir and PecS homologues in E. carotovora subsp. carotovora was not identified in this study, though these proteins of E. chrysanthemi were functional on the promoter regions of the pectinase genes of E. carotovora subsp. carotovora.

Effect of harvest seasonal and gamma irradiation on the physicochemical changes in pineapple fruit cv. Pattavia during stimulated sea shipment

Abstract Gamma irradiation is used as a phytosanitary treatment for tropical fresh fruit from some producing countries. An experiment was carried out to study the effect of gamma irradiation and season of harvest on the quality ‘Pattavia’ pineapple fruit. Fruit harvested in the summer and the rainy cool (winter) seasons were exposed to gamma radiation at dose levels of 0 and 400–600 Gy from a 60 Cobalt source and the fruit stored at 13°C and 90% RH for up to 21 days. Gamma irradiation did not affect the ratio of TSS/TA, antioxidant content, or ascorbic acid concentration. However, gamma irradiation did delay color development and also induced internal browning over 50% of flesh discolored in fruit stored for 14 days, especially harvested winter fruit. Moreover, harvesting fruit in different seasons had a significant effect on fruit quality after harvest and during stimulated sea shipment storage. The result showed that gamma irradiation can be used as a phytosanitary treatment with minor changes in eating quality. However, the internal browning was greater if fruit were stored longer than 1 week at 13°C.