Kinetics of amino acid loss in carrot juice concentrate during storage

Effect of Food Matrix Type on Growth Characteristics of and Hemolysin Production by Vibrio alginolyticus

ABSTRACT

The growth of and hemolysin production by two V. alginolyticus strains (HY9901 and ATCC 17749T) at 30°C were investigated in briny tilapia, shrimp, scallop, oyster, pork, chicken, freshwater fish, and egg fried rice. Bacteria were enumerated by plate counting. Hemolysin production was evaluated with blood agar and hemolytic titer tests. The two V. alginolyticus strains had similar growth and hemolysin production patterns in all tested foods. Based on the goodness-of-fit primary model statistics (coefficient of determination, mean square error, bias factor, and accuracy factor), the modified Gompertz model was a better fit than the logistic model to V. alginolyticus growth in foods. Growth kinetic parameters of V. alginolyticus had a higher μmax and shorter λ in the following order: briny tilapia > shrimp > freshwater fish > egg fried rice > scallop > oyster > chicken > pork. V. alginolyticus levels were similar at the stationary phase, with no significant growth difference between raw and cooked foods. Significantly higher thermostable direct hemolysin activity (P < 0.05) was found for V. alginolyticus in the following order: briny tilapia > freshwater fish > shrimp > chicken > egg fried rice > scallop > oyster > pork. However, the hemolytic titer was not consistent with the thermostable direct hemolysin activity and was significantly higher (P < 0.05) in the following order: briny tilapia > egg fried rice > shrimp > freshwater fish > chicken > scallop > oyster > pork. Contrary to current belief, V. alginolyticus produced more hemolysin in some nonseafoods (freshwater fish, egg fried rice, and chicken) than in scallops or oysters. This report is the first on the growth and toxicity of V. alginolyticus in different food matrices and confirms that some nonseafoods can be contaminated with pathogenic V. alginolyticus. These results should increase awareness of nonseafood safety issues and improve the accuracy of V. alginolyticus risk assessments.

HIGHLIGHTS

Investigations on the formation of α-dicarbonyl compounds and 5-hydroxymethylfurfural in fruit products during storage: New insights into the role of Maillard reaction

The formation of α-dicarbonyl compounds and 5-hydroxymethylfurfural was investigated under different conditions and the amino acid adducts of them were confirmed using high-resolution mass spectrometry in fruit products during storage. Changes in the concentrations of sugars, amino acids, α-dicarbonyl compounds, and 5-hydroxymethylfurfural in fruit juice concentrates and dried fruits were monitored. Among the dicarbonyls, glucosone was the dominant one in 30 °Bx of fruit juice concentrates, whereas 3-deoxyglucosone was the major in 50 and 70 °Bx of those and in all dried fruits during storage. The highest level of 3-deoxyglucosone was found as 7251 ± 896.6 mg/kg in dried date at the end of the storage. During storage, the loss of free amino acids significantly increased (p < 0.05) in the higher initial reactant concentrations in fruit juice concentrates. The confirmation of amino acid adducts of dicarbonyls and 5-hydroxymethylfurfural generally with high mass accuracy proved the contribution of Maillard reaction to non-enzymatic reactions in fruit products.