RESUMEN
A water-soluble N-alkyl semisynthetic derivative of natamycin was synthesized by the Michael addition reaction of the parent with an N-substituted malemide. A comparative study was carried out to investigate the effectiveness of the semisynthetic derivative and the parent antibiotic in suppressing mold growth on shredded Cheddar cheese stored in modified atmosphere packaging (MAP). The effects of 0-, 10-, and 20-ppm antimycotic treatments were examined. A 20-ppm natamycin treatment effectively suppressed visible mold growth (< 10(4) CFU/g) in MAP samples for up to 30 days after packages were opened. The performance of the 20-ppm semisynthetic derivative was similar to that of the 10-ppm natamycin treatment. For these treatments, visible mold growth did not occur in MAP samples until 20 days after packages were opened. These results indicate that the semisynthetic derivative of natamycin is less effective than the parent compound in suppressing mold growth on shredded Cheddar cheese.
Asunto(s)
Antifúngicos/farmacología , Queso/microbiología , Hongos/efectos de los fármacos , Natamicina/farmacología , Recuento de Colonia Microbiana , Relación Dosis-Respuesta a Droga , Microbiología de Alimentos , Embalaje de Alimentos/métodos , Hongos/crecimiento & desarrollo , Pruebas de Sensibilidad Microbiana , Oxígeno/metabolismo , Distribución Aleatoria , Factores de TiempoRESUMEN
The Limulus Amoebocyte Lysate Assay, Direct Epifluorescent Filter Technique and modified Psychrotrophic Bacteria Count were used to indicate potential shelf-life of pasteurized fluid milk. Commercial whole milk samples, stored at 7°C, were analyzed for bacterial and biochemical parameters, as well as for potential shelf-life by daily sensory evaluation. Each sample was evaluated before and after the following preliminary incubations: milk alone, milk with benzalkonium chloride, milk and broth, and milk and broth with benzalkonium chloride. The Limulus Amoebocyte Lysate Assay, Direct Epifluorescent Filter Technique, and modified Psychrotrophic Bacteria Count in conjunction with the preliminary incubations, produced relatively high correlations to shelf-life (-0.78, -0.85, and -0.86 respectively). Thus, these bacterial detection techniques could be used as rapid methods of shelf-life estimation.
RESUMEN
Raw milk samples (203) were obtained from locations throughout Virginia for the purpose of evaluating the presently available techniques, used as is or modified, for enumeration of psychrotrophic bacteria as indicators of the actual quality of milk. Each of the samples was split into two sub-samples, one being tested by various bacterial enumeration methods on the fresh sample, and the other subjected to a preliminary incubation of 13°C or 21°C for 18 h prior to bacterial enumeration. Agar pour plates and Petrifilm dry medium culture plates were both used. Results indicated that the Petrifilm technique was not significantly different from agar pour plate methods as evidenced by correlation values, mean log differences, slopes, and Y-intercepts. The Petrifilm method for the modified (rapid) Psychrotrophic Bacteria Count (mPBC) produced similar overall results (0.96, -0.283, 1.016, -0.340, respectively) to the pour plate method (0.94, 0.272, 0.865, 0.684, respectively) when compared to the standard PBC, and enumeration of colonies on the Petrifilm plates was easier due to the incorporated TTC. A modified Preliminary Incubation Count (mPIC) yielded results not significantly different from those of the PIC (0.94, 0.044, 0.991, 0.169, respectively), and was conducted in less time - 2 d vs. 3 d.