Effects of adding defective apple fermentation in rice straw on quality and microbial numbers of mixed silage

Abstract: This study aims to fully use the defective apple as rice straw resources in Xinjiang, China. Three lactic acid bacteria in different proportion were added to the defective apple, and fermented for more than 1 month to obtain the defective apple fermentation. Then, an investigation was made to evaluate whether the addition of defective apple fermentation can improve the fermentation quality of rice straw, particularly on an appropriate addition proportion. Mixed silage was carried out according to the weight ratio of defective apple fermentation and rice straw at all in straw (Ⅰ), 1:9 (Ⅱ), 3:7 (Ⅲ), 5:5 (Ⅳ), 7:3 (Ⅴ), and 9:1 (Ⅵ), and 3 replicates for each group, then they were fermented for 90 days. The pH value was measured by an acidometer, while the Dry Matter (DM) by dried at 105 ℃, Crude Protein (CP) by Kjeldahl method, Neutral Detergent Fiber (NDF), and the Acid Detergent Fiber (ADF) were determined, Water-Soluble Carbohydrates (WSC) were determined by anthrone-sulfuric acid colorimetric method, lactic acid, acetic acid, propionic acid, and butyric acid were determined by chromatographic method, and NH3-N was determined by phenol-sodium hypochlorite colorimetric method. The results showed that the addition of defective apple fermentation products improved the quality of mixed silage. The contents of CP and WSC in a rice straw increased significantly (P < 0.05). After 90 days of silage, the Lactic Acid (LA) contents from group I to Ⅵ was 0.17%, 0.85%, 1.95%, 2.43%, 2.67%, and 2.71%. Acetic Acid (AA) contents from group I to Ⅵ was 0.09%, 0.32%, 0.43%, 0.74%, 0.78%, and 0.85%, respectively. The contents of LA and AA increased with the increase of defective apple fermentation, and obviously lower in group I (without defective apple fermentation) than other groups (P < 0.05). The Butyric Acid (BA) content from group I to Ⅵ was 0.22% 0.08%, 0.05%, 0.03%, 0.09%, and 0.11%. NH3-N/TN from group I to Ⅵ was 16.28%, 8.35%, 3.01%, 2.94%, 2.66%, and 2.58%, respectively. The BA, NH3-N/TN and pH value decreased with the increase of defective apple fermentation, where in group I significantly higher than other groups (P < 0.05). The pH value, the number of yeasts and molds increased gradually, and the number of lactic acid bacteria decreased gradually under aerobic exposure environment, with the extension of exposure time. During the period of aerobic exposure, the number of lactic acid bacteria in group I was always significantly lower than that in other treatments (P < 0.05), and the number of yeasts and molds was always significantly higher than that of other treatments (P < 0.05), while the number of lactic acid bacteria in groups III and IV was always significantly higher than that in other treatments (P < 0.05), indicating that the number of yeasts and molds remained at a low level. The sensory and comprehensive scores of group I without defective apple fermentation were inferior, and those of rice straw silage groups III and IV added with defective apple fermentation were excellent. Comprehensive evaluation was as follows in order: Ⅳ>Ⅲ>Ⅴ>Ⅵ＞Ⅱ>I. Therefore, the silage nutritional values of the added defective apple fermentation were improved and the rice straw was softened. Comprehensive analysis results showed that the quality of rice straw silage can be improved by adding the defective apple fermentation in this experiment, and the appropriate proportion of the defective apple fermentation and the rice straw was between 3:7 and 5:5. The finding can provide a sound basis for utilization of biologicals.