Effect of Water Activity, pH, and Lactic Acid Bacteria to Inhibit Escherichia coli during Chihuahua Cheese Manufacture.

This study aimed to evaluate the effectiveness of pH control, water activity (Aw), and the addition of lactic acid bacteria (LAB) on the proliferation of Escherichia coli in the curd during the manufacturing of Chihuahua cheese. Milk proved to be an excellent culture medium for E. coli, allowing it to develop at concentrations up to 109 cfu/g. However, the presence of LAB, the pH control, Aw, and especially the use of the Cheddarization process during the Chihuahua cheese production proved to be important obstacles that inhibited the proliferation of E. coli under the conditions studied. Moreover, reducing the water activity of the curd as quickly as possible is presented as the most powerful tool to inhibit the development of E. coli during the Chihuahua cheese-making process.

Effect of High Temperature and UV Radiation on the Insecticidal Capacity of a Spodoptera frugiperda Nucleopolyhedrovirus Microencapsulated in a Matrix Based on Oxidized Corn Starch.

A multiple nucleopolyhedrovirus native isolate (SfCH32) of Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) was encapsulated by spray-drying in a matrix based on oxidized corn starch without and with a fluorescent brightener. The microcapsules were exposed to UV radiation (365 nm) for 0, 2, 4, and 8 h at 25 °C or temperatures of 35, 40, and 45 °C for 8 h. The data obtained with temperatures 35, 40, and 45 °C were contrasted with those obtained at 25 °C. The microcapsules were evaluated for size, shape, and insecticidal capacity against third instar S. frugiperda larvae under laboratory conditions. The 82-84.2% of the encapsulating matrix, in a dry-weight basis, was recovered as NPV microcapsules of heterogeneous shape and size. The exposure to UV radiation and temperatures reduced significantly the insecticidal capacity of tested viruses; however, such capacity was higher for microencapsulated than for non-microencapsulated viruses. The non-encapsulated virus that had been exposed to 45 °C or maintained at UV radiation for 8 h showed the lowest insecticidal activity at 5th day post-inoculation, with a larvae mortality of 25.3 and 16%, respectively. The fluorescent brightener increased significantly the insecticidal capacity of encapsulated and non-encapsulated viruses, causing a mortality of 100% at that time point, and decreased the median lethal time independently of the incubation temperature and exposure time to radiation. The findings suggested that an encapsulating matrix based on oxidized corn starch might protect the insecticidal capacity of NPV under field conditions.