动物营养学报    2022, Vol. 34 Issue (3): 1464-1475    PDF    
柑橘渣的营养特点及其在畜禽生产中的应用
李春荣 , 李小宇 , 宋代军     
西南大学动物科学技术学院, 北碚 400716
摘要: 柑橘渣是柑橘加工的副产物,含有丰富的营养物质,其中一些活性物质,如柑橘黄酮、多酚、橙皮素等,具有促生长、抗氧化、抗炎抑菌等多种作用。柑橘渣水分含量高,不易运输和储存,因此,柑橘渣在饲料工业中的利用常见的是干燥和青贮2种方式。将柑橘渣用作畜禽饲料原料,不仅减轻了环境压力,还对动物的生产性能、肠道健康以及机体免疫力等具有正向的促进作用。本文就柑橘渣的营养特点及其在畜禽生产中的应用进行综述,以期为柑橘渣的饲料化应用提供参考。
关键词: 柑橘渣    营养特点    利用方式    畜禽饲料原料    
Nutritional Characteristics of Citrus Pulp and Its Application in Livestock and Poultry Production
LI Chunrong , LI Xiaoyu , SONG Daijun     
College of Animal Science and Technology, Southwest University, Beibei 400716, China
Abstract: Citrus pulp is a by-product of citrus processing, which contains a variety of nutrients. There are some active substances contained in citrus pulp, such as citrus flavonoids, polyphenols and hesperidin, which can promote growth, anti-oxidation, anti-inflammatory, and anti-bacterial, etc. Because of the high moisture content of citrus pulp, it is not easy to transport and store. Therefore, the common utilization methods of citrus pulp in feed industry are drying and silage. Developing citrus pulp as a feed material for livestock and poultry not only reduces the environmental pressure, but also improves production performance, intestinal health, and immunity of animals. In order to provide reference for application of citrus pulp as feed, this paper reviewed the nutritional characteristics and application in livestock and poultry production of citrus pulp.
Key words: citrus pulp    nutritional characteristics    utilization mode    livestock and poultry feed raw materials    

饲料生产和利用对资源的要求很高,持续的饲料竞争、土地限制和气候变化给畜牧业带来了重大的可持续性挑战,特别是在动物源性食品消费增加导致饲料需求增加的背景下。根据粮食与农业组织(Food and Agricultural Organization,FAO)2018年统计,目前,全球约有16.5亿t谷物(占谷物总产量的35.97%)用于动物饲料。但是,已经面临许多粮食安全挑战的发展中国家将承担大部分的饲料增长需求[1]。因此,缓解人畜争粮而引起的矛盾,开发一类非常规的饲料原料是很有必要的[2]

巴西、中国、美国、印度、墨西哥和西班牙等国的柑橘产量占全球总产量的2/3,是世界上主要的柑橘生产国[3]。据FAO 2017年统计,过去几十年柑橘类水果年产量增长较快,从1960年的约3 000万t上升到2017年的1.47亿t以上,其中中国柑橘产量约占全球总产量的1/2[4]。柑橘加工业产生了大量的副产品,如果处理不当,会造成严重的环境污染[5]。柑橘渣可作为一种畜禽饲料原料,Strong等[6]研究证实,将22.5%的青贮柑橘渣添加到育肥猪的饲粮中,对猪的生长性能无影响,能将每斤猪肉的成本从1.31美元降低至1.25美元,降低了饲养成本,提高了经济效益。柑橘水果的副产品中含有多种具有生物活性的化合物,包括维生素、膳食纤维、果胶、多酚和精油等,这些化合物被报道在食品、卫生、医药、化妆品和纺织行业已经有了广泛的应用,此外,柑橘含有的上述化合物有许多药理作用,如抗氧化、抗菌、抗癌、消炎和抗糖尿病等[7]。本文主要对柑橘渣的营养特点、作为畜禽饲料原料的加工处理方式及其在畜禽生产中的应用研究进行总结归纳,以期为柑橘渣的饲料化应用提供参考。

1 柑橘渣的营养特点 1.1 柑橘渣的营养组成

柑橘渣是柑橘提取加工后的副产物,约占新鲜重量的50%,包括果皮、果汁囊、膜和芯以及种子[8]。柑橘渣的营养成分会因为品种、产地、测量手段等多种因素的不同而发生变化。近年来,许多国内外学者对柑橘渣的常规营养成分进行了测定,结果虽有差异,但是都证实了柑橘渣中富含可被利用的营养成分,如粗蛋白质、粗纤维、粗脂肪、钙、磷、无氮浸出物等常规营养成分。从文献报道可见,柑橘渣中含干物质86.28%~96.55%,总能11.10~15.07 MJ/kg,粗蛋白质4.77%~9.14%,粗纤维9.60%~15.69%,粗脂肪1.80%~3.51%,无氮浸出物63.69%~75.31%,粗灰分4.90%~7.00%,钙0.10%~3.60%,磷0.05%~0.13%[9-14],柑橘渣的粗纤维和粗灰分含量还会因其加工方式的不同而不同。Zhang等[9]的研究指出,将柑橘渣去皮之后再进行处理,导致其粗纤维和粗灰分含量分别高达40.60%和18.08%。从上面的数据可以看出,柑橘渣中无氮浸出物、钙含量较高;磷、粗蛋白质含量较低。柑橘渣中的氨基酸种类齐全(表 1),柑橘渣经过发酵处理可增加氨基酸含量。

表 1 柑橘渣中氨基酸含量 Table 1 Contents of amino acids in citrus pulp[9, 13, 15] 

柑橘渣中还含有多种矿物元素,如铁、铜、锰、锌等,100 g柑橘渣中矿物元素含量大致为钠27.78~100.00 mg,钾640.00~851.98 mg,镁80.00~142.97 mg,铁17.00~80.00 mg,锌0.26~4.79 mg,锰0.44~2.21 mg,铜0.65~1.03 mg[16-18]。柑橘类水果中富含多种维生素,如维生素C、维生素D、烟酸、叶酸、硫胺素、维生素B6、维生素A等[19],不同柑橘类水果100 g果皮中的维生素C的含量在7.83~67.36 mg,差异较大[20]表 2是不同研究所得柑橘渣中β-类胡萝卜素、维生素C、维生素E的含量。

表 2 柑橘渣中维生素含量 Table 2 Vitamin contents in citrus pulp

另外,柑橘渣中还含有多种生物活性物质,如柑橘黄酮、酚类和萜烯类物质等,具有较强的抗氧化活性、抗炎和抗菌作用[24]。因此,柑橘全果以及柑橘渣具有较高的营养价值。

1.2 柑橘渣作为饲料原料的优势 1.2.1 促生长

Almeida等[25]的研究表明,在低蛋白质饲粮中添加7.5%的干燥柑橘渣能够抑制蛋白质在肠道中的发酵代谢,改变断奶仔猪的后肠发酵模式。Crosswhite等[26]的研究发现,与对照组相比,喂食含15%青贮压榨柑橘果肉或青贮全柑橘果肉饲粮的猪饲料转化率分别提高了20.0%和13.3%。崔艺燕[27]的研究表明,与抗生素组相比,柑橘提取物组仔猪十二指肠绒毛高度有提高趋势,提高了24.16%;与空白对照组相比,柑橘提取物组仔猪十二指肠隐窝深度降低12.40%,空肠隐窝深度显著降低(降低了20.76%),回肠隐窝深度显著降低(降低了28.60%),回肠绒毛高度/隐窝深度显著提高(提高了62.60%)。王帅[28]的研究表明,在断奶仔猪饲粮中添加柑橘渣能提高断奶仔猪的血糖水平,使血清中尿素氮(UN)的含量降低,这一结果表明,在断奶仔猪饲粮中添加适量的柑橘渣可提高仔猪对碳水化合物和蛋白质的吸收与利用。饲粮中添加柑橘提取物能改善肉鸡的肠道结构,提高回肠绒毛高度以及空肠、回肠绒毛高度/隐窝深度的比值,上调小肠关键氨基酸和肽转运蛋白基因的表达,促进肠道对氨基酸的吸收,从而提高肉鸡的生长性能[29]。Guzmán等[30]研究发现,在母羊饲粮中添加40%的干柑橘渣可以提高羊奶中总酚类化合物(total phenolic compounds,TPC)的含量和总抗氧化能力(total antioxidant capacity,T-AOC),提高羔羊出生后的体重以及平均日增重(ADG)。

1.2.2 抗氧化

柑橘类水果含有多种具有抗氧化功能的生物活性成分,包括维生素C、类胡萝卜素和酚类化合物[31]。De Moraes Barros等[32]研究发现,柑橘类水果含有较高的维生素C和酚类化合物,果皮中酚类化合物的含量显著高于果肉,它们与柑橘发挥抗氧化作用密切相关。多酚有助于增加血浆中抗氧化酶的活性[33]。果皮比种子中的类黄酮含量高[34],其中黄酮类化合物具有一系列生理作用,包括抗病毒、抗炎、抗微生物和抗氧化[35]。这些生物活性成分对人体健康非常重要,能保护人体免受有害自由基的侵害[36-37]。黄酮类化合物能稳定羟自由基(·OH)、过氧自由基(ROO·)和硝基自由基(ONOO·),并且黄酮类化合物的抗氧化功效随着分子结构中羟基的数量而增加[38-39]。橙皮苷和橙皮素是主要的黄酮类化合物,具有强大的自由基清除能力,能防止脂质过氧化[40]。Li等[41]发现,橙皮苷可以吸收紫外线,降低丙二醛的生成,从而抑制紫外线诱导的脂质过氧化。橙皮苷和橙皮素可直接清除自由基,在保护DNA、蛋白质和组织免受由内部因素(如致癌基因)和外部因素(如辐射、炎症和毒素)引起的损伤方面发挥着重要作用[35]。在Ali等[42]的研究中,给烟酰胺(nicotinamide,NA)/链脲佐菌素-(streptozotocin,STZ-)诱导的2型糖尿病大鼠口服网状梭菌果皮提取物、橙皮苷和槲皮素后,与糖尿病组相比,柑橘皮提取物显著提高了肝脏中谷胱甘肽(glutathione,GSH)含量与谷胱甘肽过氧化物酶(glutathione peroxidase,GPx)、谷胱甘肽巯基转移酶(glutathione-S-transferase,GST)和超氧化物歧化酶(superoxide dismutase,SOD)活性,从而改善机体的抗氧化防御系统。大量研究表明,在肉鸡饲粮中添加橘皮和柚皮,可以通过降低硫代巴比妥酸-活性物质(thiobarbituric acid-active substance,TBARS)的含量有效地减少储存期间肉鸡大腿脂肪的氧化[43-44]

1.2.3 抗炎

炎症是一个复杂的生物学过程,是先天免疫系统对有害因素(如微生物、创伤、坏死、化学或物理因素、免疫反应或代谢应激等)对细胞和血管组织造成损害的自然防御反应或过程[45]。炎症被认为是恢复组织内稳态和功能的初始反应[46]。在各种因素的刺激下,核转录因子-κB(nuclear factor-kappa B,NF-κB)被激活,NF-κB的激活诱导细胞因子调节免疫应答,产生多种促炎介质,如肿瘤坏死因子-α(tumor necrosis factor-α,TNF-α)、白细胞介素-1β(interleukin-1β,IL-1β)和白细胞介素-6(interleukin-6,IL-6)等,引发一系列的炎症反应,造成细胞及组织的损伤[47]。酚类化合物中的黄酮类化合物广泛分布于植物中[48]。黄酮类化合物具有多种生物活性,包括抗氧化、抗癌、癌症化学预防和抗炎特性[49-50]。Ho等[51]研究表明,在体外细胞培养中试验类黄酮25~100 μmol/L浓度或橘子皮提取物试验类黄酮25~100 μmol/L或指定浓度或0.5~2.0 mg/mL浓度下,橘皮提取物对脂多糖(LPS)诱导的一氧化氮(nitric oxide,NO)、TNF-α、IL-1β和IL-6分泌的抑制率分别为90.6%、80.2%、66.7%和86.8%,橘子皮具有较强的抗神经炎能力。有研究表明,橙皮苷能够显著减少炎症介质如细胞因子、酶和黏附分子的分泌;橙皮素(3′,5,7-三羟基-4-甲氧基黄烷酮,hesperetin,Hst)作为黄酮类化合物黄烷酮亚类的一员,存在于一些柑橘类水果中[52-53],且具有抗炎作用。橙皮素能通过激活过氧化物酶体增殖物激活受体-γ(peroxisome proliferator activated receptor-γ,PPAR-γ)减轻呼吸机诱导的急性肺损伤(acute lung injury,ALI)表达,并通过阻断NF-κB通路减少炎性细胞因子的产生,对机械通气致肺脏损伤产生保护作用[54]

1.2.4 抑菌

柑橘提取物含有许多对肠道微生物群有影响的化合物,例如:柑橘类水果中存在的果胶衍生的果胶低聚糖对于双歧杆菌和乳酸菌的生长具有促进作用,也可以抑制病原菌侵入肠道[55]。Nannapaneni等[56]的研究表明,柑橘皮提取物能够抑制大肠杆菌O157∶H7的生长。有研究表明,通过圆盘扩散测定法筛选的7种柑橘精油对沙门氏菌的11种血清型菌株具有抗菌作用[57]。此外,Nannapaneni等[58]的研究表明,7个橙油组分具有抑制弯曲杆菌和弧菌属菌种生长的能力。细胞膜的破坏通常是抗菌物质的主要目标,据报道,抗菌化合物对细胞膜结构和流动性的干扰在发挥其抗菌作用方面起着重要作用[59-61]。Wang等[62]在研究中发现,柚皮素发挥抗菌作用是通过诱导3-羟基酰基(酰基载体蛋白)脱水酶[3-hydroxyacyl-(acyl-carrier protein) dehydratase,fabA]基因上调,(酰基载体蛋白)S-丙二酰转移酶[(acyl-carrier-protein) S-malonyltransferase,fabD]、3-氧酰基-[酰基载体蛋白]合酶Ⅱ[3-oxoacyl-(acyl-carrier-protein) synthase Ⅱ,fabF]、3-氧酰基-[酰基载体蛋白]还原酶[3-oxoacyl-(acyl-carrier protein) reductase,fabG]、3-氧酰基-[酰基载体蛋白]合酶Ⅲ[3-oxoacyl-(acyl-carrier-protein) synthase Ⅲ,fabH]、烯醇基-[酰基载体蛋白]还原酶Ⅰ[enoyl-(acyl-carrier protein) reductase Ⅰ,fabI]和RNA聚合酶sigma-B(RNA polymerase sigma-B factor,sigB)基因下调,导致饱和脂肪酸合成减少,不饱和脂肪酸合成增多,改变细菌细胞膜脂肪酸的组成增加膜的流动性来实现的。Wang等[63]进一步的研究发现,柚皮素通过改变苯丙氨酸、酪氨酸和色氨酸残基的微环境,引起膜脂肪酸组成和膜蛋白构象的扰动,破坏致病菌的细胞膜,从而发挥抗菌效果;对柚皮素对大肠杆菌螺旋22菌和金黄色葡萄球菌的最低抑制浓度(MIC)测定结果显示这2种细菌在暴露于1.0和2.0 MIC后均发生了形态学变化。Ebrahimi等[64]研究发现,连续42 d在肉鸡饲粮中添加0.75%的干柑橘皮能够减少盲肠中大肠杆菌的数量,对乳酸菌等的数量无显著影响。Kasim等[65]的研究发现,伤寒杆菌诱导的BALB/c小鼠口服酸橙皮提取物可直接杀灭并减少小鼠腹腔液中伤寒杆菌,降低Toll样受体4(Toll like receptor 4,TLR4)mRNA的表达。

2 柑橘渣的加工处理

柑橘渣作为柑橘产品加工的副产物,水分含量高,营养价值全面,富含多种生物活性物质,因此,可作为畜禽饲料原料。干燥柑橘渣和发酵(青贮)柑橘渣是最常见的柑橘渣饲料原料。

2.1 干燥加工

干燥柑橘渣即通过一些手段和工艺流程直接或间接的将柑橘渣的含水量降到12%以下。为了提高柑橘渣的利用率,可以通过干燥来保存。Alsaied等[66]研究发现,添加石灰可以破坏废渣中果胶的亲水性。因此,柑橘渣可以采用两步法干燥,干燥流程如图 1所示。干燥的第1步是在切碎的果皮中加入0.5%的石灰来中和游离酸结合果胶。然后有2种进一步加工的方法:1)在干燥之前,在压榨机中除去多余的水分。压榨液减压浓缩至60%或70%干物质,用作动物饲料(柑橘糖蜜);2)整个湿材料直接在旋转干燥器中干燥,这种方法在使用天然气或其他低成本燃料的地区是可行的。

图 1 柑橘渣干燥流程 Fig. 1 Citrus pulp drying process[66]
2.2 发酵利用

新鲜柑橘渣蛋白质含量低,还含有果胶等影响动物消化的抗营养成分,且含有多种苦味物质,适口性差,纤维含量高,影响动物采食量。但它有丰富可发酵底物,如糖、非淀粉多糖和有机酸等[67-70],把柑橘渣进行发酵,有利于营养成分的积累。Migwi等[68]的研究表明,在柑橘果渣中添加一些纤维素(如麦麸、家禽垫料等),基础青贮饲料中每日干物质、有机质、可消化有机物、有机物的消化率显著提高,青贮可以消灭青贮前大量存在于混合物中的大肠杆菌,总氮含量虽然不受影响,但青贮使可溶性氮的比例显著增加。Awais等[71]研究表明,用酵母对柑橘渣进行发酵能提高柑橘渣中粗蛋白质的含量,酵母发酵柑橘渣的组成为:干物质92.00%、粗蛋白质30.50%、粗脂肪4.7%、粗灰分6.72%、中性洗涤纤维20.15%、酸性洗涤纤维10.60%。Huang等[72]的研究表明,用产假丝酵母和枯草芽孢杆菌对柑橘渣进行固态发酵,其粗蛋白质、可溶性蛋白质含量分别提高54.83%和866.50%,达到(242.50±6.50) mg/g和(39.53± 1.77) mg/g,必需氨基酸和非必需氨基酸含量比对照组分别提高了230%和402%,特别是亮氨酸和苯丙氨酸含量(8.3%和5.1%,基于总蛋白),果胶、粗纤维等抗营养因子的含量分别降低了43.10%和20.21%;相关分析表明,酸性蛋白酶、中性蛋白酶、果胶酶、木聚糖酶等4种酶的活性与可溶性蛋白、总糖和还原糖含量的变化有显著性关系,说明蛋白质的富集过程与有机质和酶活性的变化密切相关。

3 柑橘渣在畜禽生产中的应用 3.1 在家禽生产中的应用

Vlaicu等[44]在肉鸡饲粮中分别添加了2%橘皮、2%柚皮,结果表明,在肉鸡饲粮中添加2种柑橘皮不仅可以延缓脂肪氧化,还减少了致病性大肠杆菌和葡萄球菌的生长,而有益菌乳酸杆菌的生长则得到了显著改善。Vlaicu等[73]的另一项研究发现,在肉鸡饲粮中添加亚麻粉(flax meal,FM)、干橙皮(dried orange peel,DOP)和干燥的红葡萄柚皮(dried red grapefruit peel,DRGP)能显著改善肉鸡鸡肉的色泽和组织结构,且不影响肉鸡胸肉的化学成分和脂肪酸组成。Abbasi等[74]为研究饲粮中不同水平的柑橘干渣对肉鸡生长性能、胴体性状、血液代谢产物、体液免疫和盲肠微生物种群的影响,在肉鸡饲粮中分别添加0、0.5%、1.0%、1.5%和2.0%的柑橘渣,结果发现,添加2.0%的柑橘渣显著提高了饲养期间肉鸡的采食量和体重,且能降低肝脏和腹部脂肪以及血清甘油三酯含量。Nazok等[75]研究了不同添加量的干柑橘浆对25~37周龄蛋鸡的生产性能、蛋品质和血液参数的影响,研究发现,16%的干柑橘浆可显著提高血浆中葡萄糖和高密度脂蛋白的含量,降低血浆中胆固醇、低密度脂蛋白和甘油三酯的含量,12%的干柑橘浆对蛋鸡生产前期的生长性能和蛋品质无不良影响。Valtierra-Rodríguez等[76]的研究表明,酸橙、李子和酸橙皮提取物的混合物可以减少鸡肉产品中弯曲杆菌污染,保障食品安全。Lien等[77]的研究中,在蛋鸡饲粮中分别添加0.05%橙皮素、0.05%柚皮素和0.50%果胶,结果表明,添加这3种物质均显著降低了蛋黄胆固醇含量。在饲喂含有橙精油的饲粮时,肉鸡体重会增加且消化道中的绒毛高度也会增加[78]。Yu等[29]在肉鸡饲粮中添加10 mg/kg的柑橘提取物,发现血浆总蛋白、白蛋白和葡萄糖含量增加,尿素含量降低,同时增加了回肠的绒毛高度以及空肠和回肠的绒毛高度/隐窝深度,降低了空肠和回肠的隐窝深度,增加了血浆大多数必需氨基酸的含量;此外,还上调了空肠中中性氨基酸转运体(neutral amino acid transporter,ASCT1)、不依赖Na+的阳离子和两性离子氨基酸转运体(Na+-independent cationic and zwitterionic amino acid transporter,B0, +AT)、神经递质转运体(neurotransmitter transporter,B0AT1)、神经元/上皮高亲和力谷氨酸转运体(neuronal/epithelial high affinity glutamate transporter,EAAT3)、与B0, +有关的氨基酸转运体(related to B0, + amino acid transporter,rBAT)、Na+非依赖性阳离子和Na+依赖性中性氨基酸转运蛋白-2(Na+-independent cationic and Na+-dependent neutral amino acid transporter-2,y+LAT2)和二肽和三肽转运体1(di- and tri-peptide transporter 1,PepT1)的表达以及回肠内B0,+ATEAAT3、rBATy+LAT2、阳离子氨基酸转运体1(cationic amino acid transporter 1,CAT1)和PepT1的表达,这些基因表达的蛋白参与了氨基酸和肽的转运,说明柑橘提取物通过上调小肠关键氨基酸和肽转运蛋白的基因表达来促进肠道对氨基酸的生理吸收,从而提高肉鸡的生长性能。

综上可知,在家禽饲粮中添加柑橘渣及柑橘渣提取物能提高家禽的采食量,改善血液指标,增加肠道对氨基酸的吸收,提高家禽的生长性能,并且改善鸡肉品质以及鸡蛋品质。

3.2 在家畜生产中的应用 3.2.1 在猪生产中的应用

Cisse等[79]在母猪饲粮中添加了柑橘提取物,结果表明,其能影响肠道微生物群,还缩短了母猪产仔至第1次排便的间隔时间,显著提高了母猪的采食量;此外,用柑橘提取物饲喂母猪,将仔猪的日增重提高了11.7%,同时降低了6.8%的饲料转化率。在Wang等[80]的研究中,在育肥猪饲粮中添加0.5、1.0或1.5 g/kg柚皮苷,对照组不添加,结果表明,所有柚皮苷添加组myhcila(调控肌肉发育)mRNA表达水平均显著升高,饲粮中添加0.5 g/kg的柚皮苷可以将育肥猪的瘦肉含量提高7.63%,眼肌面积提高21.46%,饲粮中添加1.0 g/kg的柚皮苷能够显著提高肌肉的pH和肌酐一磷酸含量,提高了猪肉的品质,此外,饲粮中添加1.0 g/kg的柚皮苷还能显著提高猪肉中超氧化物歧化酶活性和总抗氧化能力,并显著提高肝脏超氧化物歧化酶和谷胱甘肽过氧化物酶活性。

近年来,黄酮类化合物在家畜中的应用受到了广泛的关注,因为它们具有延缓脂质氧化的作用,并能改善肉质参数而不在产品中留下残留物[81]。柚皮苷是黄烷酮柚皮苷的一种糖苷,可作为主要的抗氧化剂存在于葡萄柚和柑橘类水果中[82]。Wang等[83]在研究中发现,氧化应激会降低断奶仔猪的生长性能,使其平均日增重和平均日采食量下降。Goodarzi等[84]的研究表明,在断奶后仔猪饲粮中添加柚皮苷可改善仔猪的生长性能和营养物质消化率,并且对仔猪空肠绒毛和隐窝的组织形态学状态没有显著影响。Cui等[85]的研究表明,在断奶仔猪饲粮中添加柑橘提取物可以增加十二指肠碱性磷酸酶和脂肪酶的活性,以及空肠碱性磷酸酶和胰蛋白酶的活性,血液中白蛋白含量增加了18.80%,血浆中总必需氨基酸含量增加了25.23%,苏氨酸含量升高了89.06%,十二指肠、空肠和回肠的隐窝深度分别减少了12.41%、20.76%、28.64%,回肠绒毛高度与隐窝深度的比值提高了66.67%。Pascoal等[86]的研究表明,饲粮中添加大豆壳和柑橘浆增加了仔猪空肠杯状细胞数量和绒毛密度以及胃和盲肠内容物黏度,降低了35日龄屠宰仔猪小肠中大肠杆菌的发生率,导致更高的绒毛密度。Cerisuelo等[87]的研究表明,与对照组相比,柑橘果肉组猪的肠杆菌数量较低;对于乳酸菌,研究结束时组间无显著差异。

综上可知,在猪生产中应用柑橘渣及柑橘渣提取物能够改善猪肠道菌群组成,提高抗氧化性能,改善肠道生理结构,增加肠道酶活性,提高瘦肉率以及生长性能。

3.2.2 在反刍动物生产中的应用

由于反刍动物的瘤胃具有发酵高纤维饲料的能力,柑橘渣可作为能量饲料用于配制反刍动物饲粮[10, 88]。De Felice等[89]的研究表明,在山羊饲粮中添加柠檬提取物会使真胃和胰腺中神经肽Y(神经肽Y是哺乳动物中最丰富的神经肽之一,以其促食欲作用而闻名,广泛分布在羊羔的真胃、十二指肠和胰腺中)含量显著增加,从而提高山羊的食欲。Guzmán等[90]的研究表明,用脱水橙果肉替代80%谷物饲喂哺乳母羊,提高了乳羔羊肉中多不饱和脂肪酸/饱和脂肪酸比值以及降低了n-6/n-3比值,同时羔羊肉中的挥发性物质包括乙基呋喃、二甲基二硫和庚烷的含量显著提高,提高了羊肉的感官品质。在Tayengwa等[10]的研究中给7个月龄的安格斯公牛饲喂干柑橘果肉,结果表明,干柑橘果肉提高了公牛对干物质、有机物和无灰中性洗涤纤维的表观消化率,提高了瘤胃总挥发性脂肪酸、乙酸和异戊酸的浓度,降低了丙酸的浓度,提高了乙酸与丙酸的比例。由于多酚具有抗氧化和抗菌特性,因此,饲喂富含多酚的饮食,例如,干葡萄渣(10%)或干柑橘渣替代饲粮中35%的大麦可延长羊肉的保质期[91-92],干柑橘渣(24%或35%)或用干柑橘渣替代饲粮中40%的小麦可延长牛肉的保质期[93-94]。亚油酸、C18∶2n-6、α-亚麻酸、C18∶3n-3、油酸、C18∶1n-9等多不饱和脂肪酸的含量和组成是的响肉类风味发生的主要因素[95-96]。因此,脂肪酸和挥发性成分对新鲜肉的加工、储存、运输和营销以及最终的消费者感官质量非常重要[97-99]。Tayengwa等[23]的研究表明,与对照组相比,在饲粮中添加150 g/kg的干葡萄渣或干柑橘渣增加了肥育公牛肌肉中的总共轭亚油酸(conjugated linoleic acid,CLA)、n-3和n-6多不饱和脂肪酸的比例,降低了醛、酮和醇的浓度,但不影响牛肉的感官特性。Liotta等[100]的研究表明,在绵羊饲粮中加入10%的金橘浆(blond orange pulp,BOP)可使绵羊的产奶量和羊奶中脂肪的含量增加,而奶酪样品的pH显著降低,脂肪和蛋白质含量增加。在ĺtavo等[101]的研究中,用橙皮青贮(250、500或750 g/kg,饲粮干物质基础)代替玉米青贮饲喂经产荷斯坦奶牛,结果发现,含有250和500 g/kg橙皮青贮的饲粮显示出与标准玉米青贮饲粮相似的牛奶产量和牛奶中蛋白质含量,而750 g/kg橙皮青贮作为粗饲料显著增加了牛奶中脂肪和蛋白质含量。Guzmán等[30]的研究表明,用干橙浆(dried orange pulp,DOP)替代饲粮中40%或80%的玉米会使山羊血浆中肌酸激酶和天冬氨酸转氨酶活性降低,这意味着对肌肉的氧化损伤减少。

Callaway等[102]在绵羊饲粮中分别添加0、5%、10%(干物质基础)的橘皮颗粒,结果表明,添加橘皮颗粒后大肠杆菌O157∶H7的数量在整个胃肠道都被降低;然而,在饲喂添加10%橘皮颗粒饲粮的绵羊瘤胃中,这种降低达到显著水平;大肠杆菌O157∶H7在盲肠和直肠中的数量通过添加5%和10%的橘皮颗粒饲料而显著减少。

综上可知,在反刍动物中生产应用柑橘渣及其提取物提高了反刍动物的食欲及乳品质并提高了产奶量,同时还能提高肌肉的抗氧化性能和肉的感官品质,降低肠道中大肠杆菌的数量。

4 小结

柑橘渣含有丰富的营养物质以及多种活性物质,具有促进生长、抗氧化、抗炎、抑菌等多种作用。新鲜柑橘渣因为含水量大而不易储存和运输,所以实际生产中更多使用的是发酵柑橘渣。发酵柑橘渣可以减少柑橘中的苦味物质,从而提高动物的适口性。柑橘渣及其提取物均可添加到家禽或家畜的饲粮中,在家禽饲粮中添加柑橘渣及其提取物能提高提高家禽的生长性能,改善血液指标,改善鸡肉品质以及鸡蛋品质;在家畜饲粮中添加柑橘渣及其提取物能提高家畜的食欲、肌肉的抗氧化性能和肉的感官品质,改善肠道菌群组成。柑橘渣在仔猪上的应用研究比较少,对猪繁殖性能方面的研究国内外的报道非常少也都,今后还需要增加这一方面的研究。

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