Corn is one of the most used cereals in the world. Its industrialization process in the bioethanol production generates several by-products, among them distillers dried grains, whole corn germ (WCG), the outer seed shell, and oil [1
]. These by-products can be used in animal and human feeding, biofuel and feedstock production, or other systems. The WCG is obtained from the wet degermination of corn grain by a mechanical extraction process [4
The WCG has been studied in diets for ruminants due to its crude protein (10 to 15%) [5
], ether extract (44%) [1
], and linoleic acid (56% of total fatty acids) contents [1
]. The inclusion of WCG in the ruminant diets aims to increase energy density [7
] and polyunsaturated fatty acids, to obtain higher levels of conjugated linoleic acid (CLA) in the meat, which are beneficial to human health [8
Given the importance of incorporating nutraceutical components in red meat, studies have been conducted to decrease the saturated fatty acid (SFA):polyunsaturated fatty acid (PUFA) ratio, maintaining the balance of the omega 6:omega 3 ratio [8
]. Furthermore, it is aimed to increase the concentrations of CLA in the meat of ruminants [9
]. The CLAs are biohydrogenation intermediates that, from the hydrogenation of linoleic acid by ruminal microorganisms, can pass from the rumen to be absorbed by the intestine. Subsequently, they are then incorporated into the meat of ruminants [10
The WCG contains 85% of the total lipids in the grain [11
], which is naturally protected by the pericarp. Therefore, this protection could decrease the biohydrogenation activity of ruminal bacteria on the unsaturated lipids present in the germ. Moreover, it increases the level of unsaturated lipids that will reach the intestine and, consequently, is incorporated into the meat [9
To our knowledge, there are few studies with contradictory results of the dietary inclusion of WCG as a source of linoleic acid in diets for lambs. Given the nutritional characteristics, it is hypothesized that there is an inclusion level of WCG that increases diets’ energy density for feedlot lambs, improving performance, carcass yield, and quality due to the increase of the unsaturated fatty acid deposition in the meat.
This study aimed to evaluate the effects of whole corn germ inclusion as a linoleic acid source in diets for feedlot lambs on the carcass characteristics, physicochemical composition, sensory attributes, and fatty acid profile of the meat.
2. Materials and Methods
2.1. Location and Ethical Considerations
The experiment took place at the Experimental Farm of the Federal University of Bahia, located in the municipality of São Gonçalo dos Campos, Bahia, Brazil. This study was conducted in strict accordance with the recommendations presented in the Guide of the National Council for Animal Experimentation Control (CONCEA). The protocol was approved by the Ethics Committee on the Animal Use of the School of Veterinary Medicine and Animal Science at the Federal University of Bahia (Permit number: 70/2018).
2.2. Animals, Experimental Design, General Procedures, and Diets
Forty non-castrated, crossbreed Dorper × Santa Inês lambs with an average age of 4 months and an average initial body weight (BW) of 22.1 ± 4.0 kg (mean ± standard deviation) were distributed in a completely randomized design with five treatments and eight replicates (animals).
Lambs were housed in individual, covered stalls with suspended slatted wooden floors measuring 1.2 m2 (1.2 × 1.0 m), equipped with drinkers and feeding throughs. They received water ad libitum, and the experimental diets twice daily. Before the experiment began, all animals were identified and vaccinated (rabies and clostridial vaccines). They were then allocated at random to the treatments.
The lambs were kept in the feedlot for 75 days, which were preceded by a 15-day period of acclimation to the facilities, daily management, and diets. During this phase, they received diets composed of 500 g/kg of sorghum silage (Sorghum bicolor
(L.) Moench) and 500 g/kg of concentrate mixture comprised of soybean meal, ground corn, WCG, urea, and a commercial mineral premix (Table 1
The experimental diets consisted of 0, 30, 60, 90, and 120 g/kg WCG inclusion in diets (dry matter basis). The diets were formulated to supply the nutritional requirements of growing male lambs with a gain of 200 g/day as recommended by the National Research Council [12
Animals were fed twice per day (09:00 h and 16:00 h), divided equally into two meals, as a total mixed ration (TMR). Nutrient intake was determined based on the difference between the amount of each nutrient contained in the feed offered and the feed refused during the experimental period. The amount of feed was adjusted daily, with an acceptable refusal amount about 10 to 20% of the total amount supplied to ensure ad libitum intake.
2.3. Chemical Analysis of Ingredients and Diets
During the feedlot period, samples of roughage, ingredients, diets, and refusals were weighed daily, harvested weekly, and subsequently frozen at −20 °C. At the end of the experimental period, the samples were then thawed, pre-dried in a forced-air oven at 55 °C for 72 h, and ground through a Wiley cutting mill with a 1-mm sieve. Ground samples were analyzed according to the methods of the Association of Official Analytical Chemistry [13
] for dry matter (DM; method 934.01), ash (method 942.05), crude protein (CP = N × 6.25; method 968.06), and ether extract (EE; method 920.39) contents. The organic matter (OM) content of forage and feeds was determined by the following formula: OM (% DM) = 100 − ash (% DM).
The neutral detergent fiber was determined according to Mertens [14
], using heat-stable alpha-amylase without the addition of sodium sulfite to the detergent, and acid detergent fiber (ADF) as described by Van Soest et al. [15
]. Ingredients were also evaluated for lignin (method 973.18; AOAC) [16
], by solubilization of cellulose with 72% (w/v
) sulphuric acid.
The neutral (NDIP) and acid detergent insoluble protein (ADIP) contents were determined according to the methods of Licitra et al. [17
]. Non-fibrous carbohydrates (NFC) contents were estimated according to Hall [18
] and expressed in percentage.
2.4. Slaughtering Procedures and Carcass Characteristics
At the end of the experiment, animals were transported to a commercial slaughterhouse, subjected to a 16-h fasting period, and weighed to determine the final weight (FW). They were then stunned using the proper equipment to promote electronarcosis. Then, the animals were suspended, bled from the jugular vein and carotid artery before being skinned, and eviscerated according to the recommendations of procedures for handling and humane slaughter of the animals [19
The mean pH was obtained by analyzing (in triplicate) the Longissimus lumborum (LL) muscles 45 min (initial) and 24 h after slaughter (final), using a digital HANNA skewer type HI 99163, connected to a penetration electrode, previously calibrated with pH 4.01 and 7.01 buffer solutions.
After the slaughter, carcasses were weighed to determine the hot carcass weight (HCW) and the hot carcass yield (HCY = HCW × 100/FW) and then transferred to a cold chamber (5 °C), where they remained for 24 h. Subsequently, the carcasses were weighed to determine the cold carcass weight (CCW) and cold carcass yield (CCY = CCW × 100/FW).
After the 24 h slaughtering period, the carcasses were subjectively evaluated for conformation, finishing, and fatness using a visual scale, from 0 to 5, as proposed by Cezar and Sousa [20
], and the marbling of the meats. The carcass morphometric measurements were measured according to Osório et al. [21
]. The measured parameters included the internal length, external length, leg length, leg circumference, rump width, chest width, chest depth, rump perimeter, and chest perimeter. The length and perimeter measures were taken using a tape measure, whereas those related to width and depth, with a manual meter aid.
The carcasses were cut longitudinally at the midline into two symmetrical antimeres. The carcass antimeres were sectioned between the 12th and 13th ribs to collect the loins (LL muscle) according to the methods described by Colomer-Rocher et al. [22
]. Afterward, the loin eye area (LEA) was assessed using plastic transparency sheets and an appropriate pen. Thus, the following measures were established: the length and the maximum depth of the LL muscle, in cm, measured with the aid of a ruler and calculated from the ellipse formula: LEA = (length/2 × depth/2) π, in cm2
, proposed by Silva Sobrinho [23
The subcutaneous fat thickness (SFT) in the carcasses was measured, in mm, with the aid of a digital caliper at ¾ distance from the medial side of the LL muscle, to the side of the spinous process. Subsequently, loins from the left and right sides were collected from each animal and immediately weighed, deboned, identified, vacuum packed in polyethylene packs, and stored at –20 °C for further evaluation of physicochemical analysis, sensory attributes, and fatty acid profile.
2.5. Meat Physicochemical and Sensory Analysis
Meat analysis was performed after thawing the loins in plastic bags (10 °C for 12 h). The samples were then dissected with the aid of a scalpel and knife. The color parameters were evaluated using the left side of the loins collected from the lambs. The color parameters were determined with the aid of a Minolta CR-400 colorimeter, using the CIELAB (Commission Internationale de l’Eclairage L, a*, b*) system through the coordinates of lightness (L *), redness (a *), and yellowness (b *). The colorimeter was calibrated with a white ceramic plate and illuminant C, 10°, for standard observation, and it was operated using an open cone.
Evaluation of meat color was carried out after the myoglobin was oxygenated by exposing the LL to the atmosphere for five minutes [24
]. Then, as described by Miltenburg et al. [25
], the L *, a *, and b * coordinates were measured at three different points on the muscle surface, and subsequently averaged in triplicate for each coordinate per animal.
Cooking weight losses (CWL) of LL muscle were measured in each loin sample with 1.5 cm thickness, 3.0 cm length, and 2.5 cm width cubic samples (in triplicate), free of visible connective tissue. Raw samples were weighed, placed in an aluminum-coated tray, and cooked in a preheated oven at 170 °C until the center reached 70 °C, measured using a copper-constantan thermocouple equipped with a digital reader. Subsequently, samples were cooled at room temperature and weighed again. The cooking weight loss of each sample was obtained as the difference between the weights before and after cooking [26
The Warner–Bratzler shear force (WBSF) analyses were determined using the same cooked meat samples used to measure cooking losses. At least three cores 25 mm in diameter × 25 mm in length were removed from each sample. The WBSF was measured by a texture analyzer (Texture Analyzer TX-TX2; Mecmesin, Nevada, United States) fitted with a Warner–Bratzler-type shear blade according to the standard procedure described by Wheeler et al. [27
]. The WBSF values were expressed in kgf/cm2
Evaluation of the proximate composition was carried out using the samples of LL muscles (in natura), which were lyophilized for 72 h. They were then ground using a ball mill and analyzed for moisture, ash, protein, and total lipids contents according to the methods described by the AOAC [13
The LL samples used in the sensory characteristics were evaluated using an unstructured hedonic scale of nine points by 100 untrained panelists. All panelists included 61 women and 31 men in an age group between 19 and 50 years of age accustomed to eating lamb meat. The samples were cooked on an electric grill (George Foreman Grill Jumbo GBZ6BW model) with the aid of a digital thermocouple. The thermocouple was inserted in the geometric center of each sample to monitor the temperature of each steak, which was cooked until the geometric center reached 75 °C. After cooking, the samples of LL muscle of lambs fed different WCG inclusion levels (0, 30, 60, 90, and 120 g/kg) were then cut into cubes. Afterward, they were transferred to encoded pre-heated beakers, which were placed in a water bath (75 °C) and covered with aluminum foil to ensure minimum heat loss and aroma volatiles.
The tests were carried out between 09:00 and 12:00 h, and consumers were placed in individual cabins. During the sensory evaluation, each taster was provided two samples per treatment without salt or condiments in plastic containers with coded lids; each taster also received water and cream cracker-type biscuits for intake between tastings to remove the residual flavor.
The sensory attributes of the LL muscle were evaluated using an affective method on a structured hedonic scale. The tasters evaluated the following attributes: taste, tenderness, juiciness, aroma, and overall acceptance. The scores ranged from 1 to 9, as follows: 1, disliked very much; 2, disliked; 3, moderately disliked; 4, slightly disliked; 5, indifferent; 6, slightly liked; 7, moderately liked; 8, liked; and 9, liked very much). The intensities of the lamb meat flavor and aroma characteristics were also evaluated according to American Meat Science Association (AMSA) [28
2.6. Fatty Acid Profile
The composition of lipids extracted from the samples of diets and LL was determined by converting the lipid extracts to fatty acid methyl esters (FAMEs). Afterward, FAMEs were prepared following the methodology described by O’Fallon et al. [29
Meat samples (in natura) were ground (homogenized) in grinder (Cadence 150W MDR 302), lyophilized for five days, and milled (homogenized) again. Approximately 0.5 g of dry sample was placed in a 16 × 125 mm pyrex culture tube, which contained 1.0 mL of internal standard C19:0 (189-19 Sigma Aldrich, São Paulo, Brazil; 10 mg of C19:0/mL of MeOH), added with 0.7 mL of 10 N KOH in water, 5.3 mL of MeOH. The tubes were incubated at 55 °C in a water bath for 1 h 30 min with vigorous stirring to permeate every 20 min to dissolve and hydrolyze the sample. After cooling in an ice-water bath, 0.58 mL of 24N H2SO4 in water was added. The contents of the tubes were mixed by shaking and precipitated with K2SO4. They were then incubated in a water bath at 55 °C for 1 h 30 min with shaking for 5 s every 20 min.
After synthesizing the FAMEs, the tubes were cooled in an ice-water bath. Subsequently, 3 mL of hexane was added, and the contents of the tubes were mixed for 5 min using a vortex. Subsequently, tubes were immediately centrifuged for 5 min, and supernatant with hexane containing FAME was transferred to gas chromatography vials. The vials were capped and placed at −20 °C until analyses.
The FAME composition was determined using a gas chromatograph (SPTM-2560) column (100 m–25 mm–0.2 μm pore size) with a flame ionization detector and split injector (Thermo Scientific Inc.) and the hydrogen as the carrier gas (1 mL min−1
). Nitrogen was used as the auxiliary gas. The temperature of the injector and detector was 250 °C at a 15:1 split. The initial temperature of the oven was adjusted to 70 °C; this temperature was maintained for 4 min, and gradually increased (at 13 °C/minute) until reaching 175 °C, where it remained for 27 min. Then, it was increased (at 4 °C/minute) until reaching 215 °C, which was maintained for 31 min [30
Identification of FAs was performed comparing the retention times of FAME to those of the standards (37 Component FAME Mix from Supelco Inc., Sigma Aldrich Darmstadt, Germany) and published chromatograms [31
]. The quantification of FAMEs was conducted based on the equation proposed by Sukhija and Palmquist [33
]: ((total area of the peaks - area of the internal standard)/area of the internal standard) × (concentration of the internal standard/weight of the lyophilized sample)). Fatty acid profile was expressed in milligrams of fatty acids per kg of meat (mg/kg).
The group sums, ratios, and total contents of the saturated fatty acids (SFAs), monounsaturated fatty acids (MUFAs), and polyunsaturated fatty acids (PUFAs), and the MUFA:SFA, PUFA:SFA, PUFA:MUFA, and n-6/n-3 values were calculated from the identified FA profiles.
The desirable fatty acids (DFA) were calculated according to Rhee [34
]. The activity indexes of the elongase and Δ9
-desaturase enzymes for FAs with 16 and 18 carbons were determined using the methodology proposed by Malau-Aduli et al. [35
] and Kazala et al. [36
The nutritional quality of the lipid fraction of the LL muscle, the atherogenicity (AI), and thrombogenicity (TI) indexes were calculated as proposed by Ulbricht and Southgate [37
]. The ratio of hypocholesterolemic:hypercholesterolemic (h:H) fatty acids ratio, as well as the concentrations of hypercholesterolemic, neutral, and hypocholesterolemic fatty acids, were evaluated and adapted according to Bessa [38
] and Santos-Silva, Bessa, and Mendes [39
2.7. Statistical Analyses
The experiment was conducted as a completely randomized design with five treatments and eight replicates (lambs) per treatment. The following statistical model was used:
where Ŷij = the observed value in the portion that received the treatment i in repetition j; μ = the overall mean; NLi = the fixed effect of the inclusion level of whole corn germ (i = 0, 30, 60, 90, and 120 g/kg); and εij = the effect of experimental error associated with each presupposition observation normal independent distribution (NID) ~ (0, σ2).
The data were subjected to analysis of variance and regression testing, with the freedom degrees evaluated by linear or quadratic effects. The command PROC MIXED of SAS (version 9.4, SAS Institute Inc.) was used to estimate the linear or quadratic parameters of significant models. To quadratic models, the maximum or the minimum point were obtained by making the second derivative of the quadratic model equal to zero.
The data related to sensory analysis were submitted to statistical analysis considering the WCG inclusion levels as a fixed effect and panelists as a random effect. The Poisson distribution was analyzed using the PROC GLIMMIX procedure of SAS 9.4. The variables were evaluated adopting 0.05 as the critical level of probability for type-I error.
Whole corn germ can be used up to 120 g/kg DM in the total diet for feedlot lambs without causing negative impact. Carcass and meat quality changes based on the quantitative characteristics, physicochemical composition, and sensory attributes of the meat.
The inclusion of WCG in lambs’ diets decreased dry matter intake. In this way, its inclusion increased the feeding efficiency and the possibility of better economic results because a smaller amount of feed was included in the diets during the feedlot period.
Nevertheless, if the meat industry seeks a better quality product, under the nutritional aspect, the level of 76.7 g/kg DM of WCG provides higher concentrations of polyunsaturated fatty acids in the meat, especially the linoleic acid that contributes to the increase of fatty acids beneficial to human health.