Steam treatment of rice straw
The rice straw was obtained from the agricultural field of Nanjing Agricultural University. The samples were chopped, and steam treated for 120 Sec at steam pressure of 15.5 kg f/cm2 (STRS-2). The College of Engineering Nanjing Agriculture University designed the steam explosion machine and dried treated and untreated rice straws was transported to experimental farm.
Location and description of the study area
The experiment was conducted at the goat farm situated at Liuhe Animal Science Base of Jiangsu Academy of Agricultural Science, Zhuzhen, Nanjing, China. There is mean annual temperature of about 28°C (82 °F) in July, while -7C (19F) in January months respectively. Moreover, this area has an approximately 1,100 millimeters (43 inches) average rainfall, 117 rainy days and have almost 76% mean relative humidity.
Animals’ management and feeding
The experiment was conducted according to the animal care and guidelines of the Animal Care Committee, Nanjing Agricultural University China. Ten Xuhuai goats (18.47±0.39 kg) were equally divided into two feeding groups and were assigned to untreated (UTRS) or steam treated (STRS) rice straw diets (Table 1) in a 60-day trial period, a 7 day adaptation period was provided to the goats prior to start of the trail. The goats were kept in a 15′×20′ shed with height at center 10′, side walls of chain link fencing 6′, slatted floor, troughs used for feeding and a central alley. Goats were offered feed on ad libitum twice daily at 08:30 and 16:30 hour (h).
Meat sampling and carcass traits
At the end of 60 days trail all the goats were individually weighed and humanely slaughtered after an 18 h fasting. After slaughtering animals were hanged for skinning which was removed in order head (up to the atlanto-occipital joint) forefeet and hind feet up to the carpal-metacarpal joint and the tarsal-metatarsal joint respectively. The muscle samples were subsequently taken from left side of carcass. A sample of about 50gm from left side longissimus dorsi (LD) muscle was taken and at -20°C stored for further analysis. Fasted live and carcass weight were recorded immediately after slaughtering and the dressing percentage was calculated by dividing the carcass weight with live weight and expressed as a percentage (%).
Muscle pH and color
The digital pH meter (Hanna, Model HI9918, USA) was used to measure the pH values of meat samples. The pH value was recorded at 45 min of post-mortem as pH 45 min, and pH 24 h at 24 h of post-mortem on the muscle (longissimus dorsi) after equilibration to room temperature. The calorimeter (Konica Minolta, CR -400, Japan) was used to assess the color of muscles for lightness (L*), redness (a*) and yellowness (b*).
Chemical analysis of meat
Moisture contents of meat were estimated by the loss in weight of 3 g minced meat and the LD muscle samples were dried for 48 h in oven at 105°C. The dried samples were aged in a muffle furnace at 550 °C for 8h and the ash contents were recorded. Analysis of crude protein (CP) by using 1 g of sample following Kjheldahl method as detailed in the AOAC (2000). The total fat contents were determined from 5 g samples in a Soxhlet apparatus following a 6-cycle extraction with petroleum ether.
Measurement of lipid oxidation
The lipid oxidation was evaluated by measuring Thiobarbituric acid reactive substances (TBARS) by utilizing malondialdehyde (MDA) standard with the help of chemical diagnostic kit (Nanjing Jiancheng Bioengineering Institute, Nanjing, China) and values were expressed as nmol/mg protein.
Fatty acid profile
Muscle samples were taken gently, and external visible fat was removed. The samples were ground homogeneously to estimate fatty acid composition. The total lipids were extracted following the chloroform-methanol procedure. Extracted lipids were trans methylated into fatty acid methyl esters and isolated by Gas Chromatograph using a Shimadzu GC-2010 equipped with CP-WAX 30M I.D.0.32 mm capillary column. The nitrogen and hydrogen were used as carrier and fuel respectively whilst the air as a combustion-supporting gas were used at constant flow rate of 3, 47 and 400 ml/min, respectively. Spilt ratio was 1:10 and 1 μl was injected. The detector and injection port were maintained at 250 °C.
The fatty acids were calculated individually according to the relation of peak area to the total area. The fatty acids were denoted as the part of each individual fatty acid to the total of all fatty acids present in the sample. The combinations and ratios of fatty acids were calculated as desirable fatty acids (DFA), total saturated fatty acids (SFA), total unsaturated fatty acids (UFA), total monounsaturated fatty acids (MUFA), polyunsaturated fatty acids (PUFA), UFA/SFA and PUFA/SFA, respectively.
Statistical Analysi
The statistical analyses were performed by using software (SPSS 16.0 K for Windows, Chicago, IL) and the obtained data were expressed as the means ± SEM values. The mean values were compared by One-way analysis of variance technique and significant difference at (P< 0.05) among the means were found by Turkey’s comparison test.