Study On Fermentation Properties In Whole Grain Brown Rice Milk With Lactobacilli

In this paper, the fermentation characteristics of lactobacilli including Lactobacillus plantarum, L.rhamnosus, L.acidophilus, L.casei in brown rice milk were studied. The pH value, titratable acidity, the viable count of lactobacillus, STS, proteolytic activity and rheological properties of brown rice milk fermented by single strain, double and multiple strains were determined in the duration of storage at 4 ℃ for 21 d. The strain and strains which showed better properties were screened initial, then the sensory quality of fermentation products was judged. According to the index, the better single strain and composition of strains for fermenting brown rice milk were selected. The chemical index, microorganism index, microstructure and flavor substance of fermentation milks selected were investigated. The main conclusions were drawn as followed:1.The results of fermentation for single strain: it showed that every strain could tolerate the acid and bile of certain concentration. L.rhamnosus could be suitable for the production of fermented brown rice milk. The viable count of lactobacillus exceeded 8 lg CFU/g during storage at 4 ℃ for 21 d, the viable count of Lr was more. The pH value of Lr was 4.45~4.5 during whole storage periods and pH was more stable. The sample fermented by L.rhamnosus displayed weak post acidification. The product fermented by L.rhamnosus had low score of STS. The proteolytic activity of Lr was 0.74~0.76 mmol/L. The four samples were well in viscoelasticity. In addition, the area of hysteresis loop of Lr was 687.92 Pa/s, and the fermented brown rice milk could recover more easily when it broken. Besides, the specimen fermented by L.rhamnosus had the property of solid.2.The products fermented by co-culture got results as following: the pH value of LrLc was 4.55~3.9 and LaLc was 4.52~3.97, the titritable acidity of LrLc was 36.07~64.21 oT and LaLc was 34.43~58.02 oT, so the post acidification was weaker. The numbers of lactobacilli were more than 8.5 lg CFU/g for all groups during storage at 4 ℃ for 21 d, LrLc was more in addition. The STS was less than 30%, the sample who was better in water holding capacity was LrLc and until 21 st the STS of LrLc fell to 14.53%. The free amino acid changed from 0.68 to 0.76 mmol/L. Rheological measurement indicated that the viscosity of LpLa, LrLc was better. In consequence, the co-culture of L.rhamnosus and L.casei gave fermented milk proper acidity, stable texture, more viable count and was fit for the fermentation of brown rice milk.3.The consequence of fermentation milk about three strains was as follows: the weakest group about post-acidification was LpLaLc, the pH value was 4.52~3.81, the titratable acidity was 39.59~69.21 oT in storage period. The viable cells numbers reduced after 21 day at 4 ℃, but the numbers were many for all the fermented milk. LpLrLc, LpLaLc reached to 9 lg CFU/g among all groups, and they declined to 8.7 lg CFU/g at last. Also the STS decreased as time went on, LpLaLc was lower and it was 14.96% at 21 st. The fermented milks of multiple strains were more in free amino acid than single and double strains. The mean was about 0.8 mmol/L, LpLaLc came to 0.86 mmol/L. The area of hysteresis loop of LpLrLa and LpLaLc was 500.98, 518.03 Pa/s, shear thinning was weaker in keeping with fitting result. As a consequence, LpLaLc was better.4.The quality assessment of fermented milk: sensory evaluation results showed that Lr and Lc, LrLc and LpLc was non-significant(P>0.05) and Lr, LrLc, LpLaLc got higher score among all fermented milk after 1 d at 4 ℃. Then the sensory evaluation was evaluated for above five species fermentd milks at 4 ℃ for 21 d and Lr, LrLc and LpLaLc were better, in other words they could be more acceptable easily. Aberration index indicated that the change of color could be ignored for the three species during storage. Microorganism index satisfied GB19302-2010 and presented network. The flavor compenent of LpLaLc was more and it has 23 kinds flavor compounds. Lr and LrLc were similar in aroma. After fermentation the products became more favourite, such as diacetyl, acetion, acetic acid and so on were produced.