The aim of this work was to optimize the osmotic dehydration (OD) as a pretreatment before hot air drying (HAD) in Nopal pads. A Box–Behnken experimental design was used to optimize the OD conditions with respect to physicochemical and chromatic parameters, and mechanical properties of Nopal pads. Factors studied were: Three concentrations of sucrose (30, 40, and 50°Brix), calcium lactate (1, 2, and3%), and immersion time (1.5, 2.5, and 3.5 hr). Results showed that sucrose concentration and immersion time were the variables with higher influence. Quality properties mentioned before and the final mineral content of the dried samples (at 60°C for 48 hr) were analyzed. The combined drying (OD + HAD) reduced the moisture content in the range of 23% to 30% compared to HAD alone. It was found that the optimization of OD allowed preserving the quality properties, being a good alternative to give an added value for dried Nopal pads. Practical applications Nopal has important bioactive properties for both humans and animal diets, since it is a rich source of vitamins, minerals, and fibers. However, the main problem of its production is that post harvesting waste is greater than 50%. For this reason, there is a great interest to study inexpensive preservation methods that allow keeping the main attributes of processed fruits. The osmotic dehydration (OD) and the hot air drying (HAD) are two simple and inexpensive techniques which can be applied by both the food industry and small‐scale food producers. In the present study, the optimization of OD as a pretreatment before HAD was a reliable tool to preserve the quality properties of Nopal pads.

ResumenEl objeto del presente trabajo fue estudiar la influencia de la temperatura sobre la frescura de la caballa (Scomber japonicus) asociada con los cambios químicos y los atributos organolépticos de los ejemplares conservados en diferentes condiciones. La calidad del pescado se determinó por evaluación sensorial mientras que la inocuidad se estableció midiendo el contenido de histamina a 6 ºC durante una semana realizando el muestreo después de transcurridos uno, tres, cinco y siete días en condiciones de refrigeración. A la temperatura ambiente de 20 ºC el muestreo se efectuó diariamente durante tres días. Las caballas refrigeradas superaron los niveles aceptables de histamina al tercer día antes de ser rechazadas por los panelistas sensoriales. Cuando las muestras se mantuvieron a temperatura ambiente alcanzaron niveles peligrosos de histamina al segundo día en coincidencia con el rechazo determinado por el panel de evaluación sensorial.Palabras clave: histamina, caballa, Scomber japonicus, refrigeración, evaluación sensorial. Influence of Storage Temperature on Histamine Formation in Mackerel (Scomber japonicus) AbstractThe aim of the present work was to study the influence of storage temperature on the freshness of mackerel (Scomber japonicus) associated with chemical changes and organoleptic attributes of the samples maintained under different environmental conditions. Fish quality was assessed by sensory evaluation while safety was determined through histamine development during refrigerated storage at 6 ºC during a week, sampling for analysis after periods of one, three, five and seven days. At room temperature of 20 ºC samples were analyzed daily during three days. Refrigerated mackerel became unsafe for human consumption, reaching unacceptable histamine levels after three days, before being rejected by the sensory panel. At room temperature samples were discarded due to their high histamine content on the second day, in agreement with the rejection decision of the sensory evaluation panel.

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