Effects of Addition of Glucose and Sorbic Acid on the Fermentationi Quality of Guineagrass(Panicum maximum Jacq.) Silages

Abstract

This experiment was carried out to study the effects of adding glucose or sorbic acid or both on the fermentation quality and residual mono-~nd disaccharides compositions of guineagrass silages. Guineagrass was treated with glucose (G) at the rates of O, 0.5, 1.0 and 2.00/0, with or wlthout sorbic acid (S) at the rate of 0.10/0 on the fresh weight basis. After thorough mixing, the grass material was ensiled into a laboratory silo (1 liter capacity) in triplicates and kept at the ambient temperature of 25 'C, followed by being opened after 30 days of storage. Except for the silage with no addition, all silages were well preserved as judged from their Iow AN/TN (35.88-77.5lg/kg) and no or only detectable level of BA, VA and PA. Adding S alone showed a small decrease in pH value, however, a significant increase in LA content and signiflcant decreases in AN/TN and VFAS content as compared with control. These suggested that S alone was effective in inhibiting the growih of clostridial and other aerobic bacteria, and decreased the protein degradation and the production of BA and VFAs, whereas increased LA content. However, the improvement was smaller than the other treatments (G or G with S) , which was attributed to the low content of WSC in the original giass. All glucose addition silages (G or G with S) Iargely improved the fermentation qualities, as indicated by significantly lower pH (3.78~.25), AN/TN (35.88-71.08g/kg) and VFAS (9.00-28.99g/kg), and the absence of BA, VA and PA, whereas signlfrcantly higher LA (24.47-52.53g/kg) and LA/AA (1.06-5.89), when compared with control. Increasing the rate of glucose addition resulted in further decreases in pH, AN/TN and VFAS and further increases in LA and LA/AA. There were not significant differences in the fermentation qualities between 20/0G and lo/oG and between S+ 20/0G and S+ IoloG, respectively, except for a large decrease in AN/TN value and a slightly but significantly higher residual glucose and mono-and disaccharides when the G Ievel was 20/0. Similarly, there were not signfficant differences in the fermentat.ion qualities between G alone and G with S, however, G with S addition tended to decrease AA content and tended to increase LA content and LA/~. Moreover, S + 20/0 G had slightly but significantly higher residual glucose and total mono-and disaccharides contents as well as signiflcantly lower ethanol content cc)mpared with 20/0 G. These suggested that the S addition inhibited the aerobic bacterial growih and saved the fermentation substrates for LAB. From the present study, it was suggested that loloG or S + Io/o G addition was effective for improving thd fermentation quality of guineagrass silage.