نوع مقاله : مقاله کامل علمی پژوهشی
نویسندگان
1 گروه علوم و صنایع غذایی، دانشگاه آزاد اسلامی واحد تهران شمال
2 زیست شناسی - دانشگاه ازاد اسلامی واحد تهران شمال
چکیده
کلیدواژهها
عنوان مقاله [English]
نویسندگان [English]
Background and objectives: Bacillus cereus is one of the foodborne pathogens in food. Today, by international standards, post-baking foods have to be cooled to less than 10 degrees Celsius for 60 hours. In this study, the effects of this parameter on cooling duration, moisture content, percentage of broken rice and rice sensory evaluation and the extent of Bacillus cereus growth were investigated.
Materials and methods: Iranian rice (Tarom) and foreign rice (Thai rice) were cooked under the same conditions. Four trays with various dimensions were prepared to achieve the rice's thicknesses of interest (i.e. 5, 7, 9, and 11 cm). Grains of rice with foregoing thicknesses were weighted using the scale and then cooled in the blast chiller fitted with a data logger. Two strains of mesophilic Bacillus cereus lyophilized (Code: FORC-005) were purchased from Takgene Co. (TAKGENE PROBIOTIC PRODUCTS). Bacteria were grown on the MYP medium to be activated according to the manufacturer's instructions. Probably occurred Bacillus cereus cells were counted per each plate following confirmation of chosen colonies. Data were analyzed through performing a one-way ANOVA in SPSS using DUNCAN post-hoc test.
Results: The results showed that increases in the thickness of rice layer increased the population of Bacillus cereus but not beyond the standard range (0.5 cfu / g). Moreover, the highest bacterial populations in Iranian and foreign rice with layer thickness of 11 cm were 0.41 and 0.3 cfu/g, respectively. In addition, increases in the thickness of layer of the studied rice exponentially increased the cooling duration. Since the cooling duration of foreign rice with the thickness of 11 cm (267 min) exceeded the required standard of 4 h, rice layer thickness greater than 11 cm will not be acceptable for cooling foreign rice. It should be noted that increases in the thickness of the samples of rice layers reduced the percentage of broken rice (by 8 and 4/9%) and the percentage of moisture loss (by 48.7 and 47.2%) in Iranian and foreign rice, respectively. In sensory evaluation, the Iranian and foreign rice received the scores of 9 and 7.9, respectively. which indicated that the Iranian rice had higher quality than the foreign rice in this evaluation.
Conclusion: Generally, the results revealed that the size of the Bacillus cereus population (colonies) expands with an increase in the thickness of rice samples (Tarom and Thai rice), but it did not exceed the standard threshold. When exceeding the standard cooling time of 4 hours, thicknesses greater than 11 cm will not be admissible for the cooling process. Importantly, as the rice thickness rises, taste characteristics in cooked rice will be less affected and more acceptable. In this study, Iranian rice (Tarom) missed less moisture content than foreign rice (Thai rice) due to textural and strain-related characteristics and ultimately was more acceptable
کلیدواژهها [English]
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