| Fermented rice cake is a kind of Chinese traditional fermented food, very popular in China especially in the southern areas. It is characteristic for its pleasant flavor, soft texture, and excellent nutrition properties. Because the water content of fermented rice cake is high, the shelf-life is short, which severely restricted its sphere of circulation, and can not meet the needs of industrialization. In this study, the dominant spoilage bacteria in fermented rice cake during storage was isolated and identified, and the change of bacterial flora was analyzed. Through choosing preservation, storage temperature, modified atmosphere packaging and high obstructing packaging films, an effective preservation technology was developed, which can extend the shelf-life of fermented rice cake. The flavors of homemade and commercial fermented rice cakes were compared by HS-SPME-GC-MS method to analyze the characteristic flavor of fermented rice cake. In addition, the quality standard of fermented rice cake was developed to promote the standardization production, as well as effectively control its quality. The main foundings are as follows:(1) The microbe of fermented rice cake during storage was studied, and the bacterial strains were identified with sequencing of partial 16S rDNA polymerase chain reaction (PCR) amplification. The results showed that bacteria were the main factor that resulted in the spoilage of fermented rice cake. Lactobacillus fermentum, Staphylococcus pasteuri as well as Bacillus cereus were isolated, purified and identified; thereinto, Lactobacillus and Bacillus were the dominant spoilage bacteria, and both of them showed a noticeable rising trend with the storage time extending.(2) Comparing the preservative effect of several preservatives,0.4g/kg of sodium acetate dehydrogenation was found be the best preservative. The preservative effects of different modified atmosphere packaging and packaging films were assessed, and the results showed that samples with BOPP/PVDC/PA/CPP composite film and filled with 100%nitrogen had the best preservative effect. Also, the shelf-life of samples stored at 4℃and room temperature was compared. It showed that refrigerated samples had a longer shelf-life. According to Siyi Lv’s study (Siyi Lv,2010) about anti-aging of fermented rice cake, this study used 1.5g/kg sucrose fatty acid esters(SE) as anti-aging agents. Therefore, the optimum storage technology was:samples adding 1.5g/kg of sucrose fatty acid ester and 0.4 g/kg of sodium acetate dehydrogenation, packaged with BOPP/PVDC/PA/CPP composite film and filled with 100%nitrogen, and stored at 4℃. In this way, the fermented rice cake after re-steamed can keep a good taste, flavor color and appearance at least in 71 days.(3) The volatile components of fermented rice cake were analyzed by HS-SPME-GC-MS method. The factors that affect the extraction efficiency were optimised, including fiber, extraction temperature and time. The optimum extraction condition was:extracting 40 min at 60℃by DVB/CAR/PDMS 50/30μm fiber. The flavors of a homemade and eight commercial fermented rice cakes were compared and analyzed. Total of 46 volatile compounds were identified in these samples. Of these, eight of them were found almost in all the samples:phenylethyl alcohol; nonanal, decanal; hexanal; octanal; d-Limonene; octanoic acid,ethyl ester, Furan,2-penty. Phenylethyl alcohol accounted for the largest proportion, which was the main flavor compound. In addition, the different compounds have different aroma, including flowers, fruits, bread and other pleasant fragrances, which together constitute the unique flavor of fermented rice cake.(4) Developed the quality standard of fermented rice cake to promote the standardization production, effectively control its quality. |
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