I.INTRODUCTION
Ensiling is the process used for preserving forage crops (Wilkins et al., 1999), which known as silage. Silage confides on the amount of sufficient organic acid production for the inhibition of unwanted microbial growth under anaerobic condition (Imai, 2000). Now a day, silages are commonly preserved forages in many countries including Korea, Japan and China. In this process, the water-soluble carbohydrates are fermented into organic acids predominantly lactic acid by homo and hetrofermentative LAB (Filya et al., 2007). Forage silages stored with lactic acid bacteria (LAB) is a significant factor in determining the quality of the silage. The selection of potent lactic acid bacterial strain in national and international research is being done actively (Ely et al., 1981; Stokes, 1992). The genus Lactobacillus is gram positive and plays important role in the dairy industry as potential food quality maintainer and fermenting agent of dairy products (Cai et al., 1999). Fermentation by lactic acid known as homolytic fermentation is the enviable type than other fermentation while the recoveries of dry matter and energy are higher (Cao et al., 2010). Lactobacillus strains have been used as a starter in the preservation of dairy products, vegetables, and fish for decades. The organic acids which produced by LAB responsible for reducing pH (Weinberg et al., 2002) and inhibition of the activities of plant enzymes and pathogenic or spoilage bacteria that could decrease the nutritive values of the silages (Weinberg and Muck, 1996). LAB in the silage distribution is a potential factor in interpreting the silage fermentation characteristics. Especially the distribution of fungi in silage preparation decrease the silage quality (Weinberg et al., 2002; Filya 2003a,b). Further, fungi are the factor that results in the cattle disease because the toxins produced by secondary metabolites of fungi. Natural populations of Lactobacillus strains on plant materials especially forage crops are often low in number. Hence, Ensilation has the way for adding fast-growing homo fermentative Lactobacillus using microbial inoculation to dominate the fermentation and thereby producing higher quality silage (O’Brien et al., 2007). The bacterial strains such as Lactobacillus Plantarum, L. acidophilus, L. fermentum, L. brevis, L. rhamnosus, L. reuterin, Enterococcus faecium and Pediococcus acidilactica are commonly used in the homo fermentative process and available in commercial inoculants as single strain or the combination of strains (Nishino et al., 2003).
Silages from IRG, rye, whole crop barely, whole crop rice etc. are commonly used to feed livestock in Korea (Ilavenil et al., 2014). Even though high protein content of the above silages, there is some difficulty to ensile with good quality because of their low fermentable carbohydrate content, complete removal of air during ensiling by tubular hollow stems and high buffering capacity (Saarisalo et al., 2007; Muck et al., 2007). These obstacles during ensiling would be overcome by using Lactobacillus inoculants with possible chemicals and enzymes and the preservation of IRG, corn, rice and barley silages could be enhanced simultaneously. It is evident that the pure culture of Lactobacillus plantarum could not be used as silage inoculants because of its poor cell growth and fermentation metabolite production. Hence, L. plantarum could be used along with other species. However L. plantarum is the commonly found natural microflora of fermented foods, it could be used as a starter or adjacent culture, in improving organoleptic quality of the final products (Moon, 1983; Tyrolova and Vyborna, 2008). Recently, Valan Arasu et al. (2014a) and Valan Arasu et al. (2013) report that L. plantarum KCC-10 and KCC-19 isolated from forages interestingly showed best antifungal and probiotic effects. Therefore, the objective of this study was to evaluate the potential role of L. plantarum KCC-10 and KCC-19 on quality and fermentation characteristics of IRG silages.
II.MATERIALS AND METHODS
1.Collection and preparation of silage
IRG was harvested at the early flowering stage at live stock farm, National Institute of Animal Science- RDA, Cheonan. Initially, two hundred grams of IRG were packed in an air-diffusible bag which served as control and three set of two hundred grams of IRG weighed and was packed in three different air diffusible bags. Subsequently, silage was manufactured with the addition of fermentative additive containing L. plantarum KCC-10 and KCC-19. Each L. plantarum (1.5×1010cfu/g) was dissolved by distilled water (0.004 g/10ml) and inoculated with the 200 g of silage. Silage was sealed to prevent air flow. Each of the samples with or without strains was prepared in triplicates. Silage was stored in room temperature for 45 days. The nutritive values, microbial counts and fermentative metabolites were analyzed. Fresh culture of KCC-10 and KCC-19 were inoculated in mass cultivation medium containing glucose 1%, soy peptone 0.25%, yeast extract 1%, MgSO4 0.01%, MnSO4 0.04%, NaCl 0.1%, CaCO3 0.2%, Na2HPO4 0.6% in a fermenter. After mass cultivation, the cultures were freeze dried. The powder form of KCC-10 and KCC-19 was used in silage preparation.
2.Nutrient composition and analysis
The content of crude protein was quantified by standard procedure (AOAC, 1990). Neutral detergent fiber (NDF) and acid detergent fiber (ADF) were analyzed according to the methods described by (Van Soest et al., 1993). Total digestible nutrient (TDN) was calculated as follow; 88.9- (ADF% × 0.79) (Holland et all., 1990; Seo et al., 2010). Samples were ground and passed through a 1 mm sieve prior to analysis. The in-vitro dry matter digestibility (IVDMD) was analyzed by the modified method of Moore (1970).
3.Enumeration of microbial populations
Ten grams of wet silage samples were transferred into sterile flasks containing 90 mL of sterile water. Then it was kept in an orbital incubator shaker at 150 rpm for 30 min and then made a tenfold serial dilutions with water (Miller and Wolin, 1974). For enumeration of LAB colony, the diluted sample (0.1 mL) was spread on selective media (Rogosa, and Sharpe agar (Diffco) and Bromocresol purple blue agar medium) and incubated at 28 ± 1 ℃ for two days. Yeasts and molds were enumerated on 3 M petrifilm (3 M Microbiology Products, St.Paul, USA), and following aerobic incubation at 28 ± 1 ℃ for four days. Fungi were enumerated on Potato Dextrose agar (PDA) [4 g/L of potato starch (Diffco), 20 g/L of starch (Difco), and 20 g/L of agar (Difco)] following aerobic incubation at 28 ± 1 ℃ for four days.
4.Analyzes of fermentation metabolites
10 g of sample was weighed and blended with 90 ml of deionized water for 24 hr in a refrigerator at 4 ℃. Firstly, samples were filtered through the filter paper (Whatman No. 6) and the filtrate was re-filtered using 0.22 ㎛ syringe filter before injection of samples in high-performance liquid chromatography (HPLC; HP1100, Agilent Co. USA). The pH of the supernatant was measured after centrifugation using a combination electrode. The filtrate was stored at - 70 ℃ with and without stabilization with 5% metaphosphoric acid (final concentration). Lactic acid content was analyzed by HPLC. The contents of acetic acid and butyric acid were analyzed by Gas Chromatography (GC-450, Varian Co., USA) method described by Kristensen et al. (2007).
5Statistical analysis
Samples were analyzed in three replicates and analysis of variance were performed on all the variables measured using SPSS/PC (Statistical Package for the Science, ver 12.0. USA). The Duncan’s multiple range tests were used to determine the effect of inoculants on the quality of IRG silage. Tests were run at the 5% probability level.
III.RESULTS AND DISCUSSION
In the present study, the consequence of L. plantarum KCC-10 and KCC-19 on improving the quality of IRG silage was observed. By analyzing the parameters such as fermentative acids, nutritive values and microbial counts of IRG silages will give the initiative of silage quality. Organic acid producing microorganisms such as Lactobacillus and other Bacillus species have been isolated from the rumen, silages and fermented foods (Giraffa et al., 2010). Generally silages from IRG, rye and alfalfa have been fed to the live stocks (Cooke et al., 2009) in South Korea and other countries. Now a day much interest is given for the preparation of silage using IRG, barley, rye with legumes because of its low cost compared to concentrated feed, but the nutritive values have been varied by the preparation technique. On the other hand, the addition of probiotic strain such as L. palntarum in the silage enhances the nutritive value of the silage and this is known as ensiling method (Avila et al., 2010).
The nutritive values of IRG silage using L. plantarum KCC-10 and KCC-19 as inoculants have been presented in Table 1. There was a slight increase in CP level observed in L. palntarum KCC-10 and KCC-19 inoculated silage compared to control. Hence, it is well known that ruminal protein degradation increases with increasing CP content in the diets (Olmos Colmenero and Broderick, 2006), but addition of inoculants like homofermentative LAB can lead to the reduction of protein breakdown in silage (Merry et al., 2000). Similarly, the slight difference was noted in the ADF content between LAB applied silages and control silage. The NDF, TDN and IVDMD contents of silages were consistent, ranging from 59.12~59.52%, 67.19~67.82%, and 58.40~59.13% respectively. Therefore, no significant changes were noted for NDF, TDN and IVDMD among the treatments (Table 1).
The number of microbial colonies in the IRG silages has been presented in Table 2. The IRG alone arbitrated group silage exhibited (p<0.05) lower number (104×107 CFU/g) of LAB compared to KCC-10 (208×107 CFU/g) and KCC-19 (166×107 CFU/g). There was a probable difference in LAB colony noted between KCC-10 and KCC-19 inoculated silages. Additionally, the number of yeast colonies in the experimental groups showed potent growth in KCC-10 supplemented silages. Further, no fungal growth was noted in the both control and experimental group and this accommodate the possible upgrade of silage fermentation with the major recovery of dry matter (Jatkauskas and Vrotniakiene, 2004).
Changes in pH and organic acids in IRG silage with KCC-10 and KCC-19 is given in Table 3. Most of the silages are susceptible to aerobic deterioration during warm climates (Danner et al., 2003). This may due to the activity of aerobic yeast that is more active in the temperature range between 25~30˚C (Ashbell et al., 2002). This problem could be solved by the addition of L. plantarum as inoculants (Danner et al., 2003). Accumulation of homofermentative LAB will increase the lactic acid and acetic acid production and thus reducing the pH of the medium. Similarly, the amount of lactic acid produced in the L. plantarum KCC-10 and KCC-19 supplemented silages were higher (p<0.05) than the control silage. Especially, L. plantarum KCC-19 supplemented silage showed a significant difference compared to the control. Further, the pH of the LAB supplemented silages were lower than the control silage, particularly L. plantarum KCC-19 applied silage had lowest (p<0.05) pH. Additionally, there is notable production of acetic acid and very little butyric acid in the LAB inoculated silage with full Flieg’s score which plays a significant role in the aerobic stability of silage (Filya et al., 2002). This favors improving silage fermentation and the reduction of less significant end products such as ammonia as well as volatile fatty acid, which can cause poor feed conversion and high dry matter loss (Avila et al., 2012). Hence, simultaneous production of lactic and acetic acid jointly with less residual butyric acid is potential factor for aerobic stability in silages (Ilavenil et al., 2014). Hence, supplementation of homo fermentative L. plantarum KCC-10 and KCC-19 with the IRG silage could be a cost-effective method for producing high-quality silage to meet the feed demand of live stocks in the growing countries.
