摘""要:椰粕(coconut"oil"residue,"COR)和椰麩(coconut"milk"residue,"CMR)是椰肉2種主要加工副產(chǎn)物,分別在椰油和椰奶加工過(guò)程中產(chǎn)生,為探究2種椰肉加工副產(chǎn)物的加工適宜性,對(duì)其營(yíng)養(yǎng)和理化特性進(jìn)行了全面分析。結(jié)果發(fā)現(xiàn),COR的脂肪含量(19.37"g/100"g)要低于CMR,而蛋白質(zhì)(11.32"g/100"g)、總膳食纖維(63.92"g/100"g)、可溶性膳食纖維(4.42"g/100"g)等營(yíng)養(yǎng)成分以及多糖(25.67"mg/g)、黃酮(4.21"mg/g)、總酚(1.15"mg/g)等活性成分含量均高于CMR。COR與CMR的水解氨基酸種類(lèi)相似,但含量存在明顯差異,其含量分別為94.955、56.975"mg/g。理化特性方面,不同溫度下COR均比CMR顯示出更好的水合特性,但二者的流動(dòng)性均較差。COR比CMR具有相對(duì)較高的熱穩(wěn)定性、較完整的晶體結(jié)構(gòu)和較高的基團(tuán)活性。綜上,與CMR相比,COR的營(yíng)養(yǎng)成分和活性成分更加豐富,水合特性和流動(dòng)性也具有相對(duì)優(yōu)勢(shì),且具有較高的熱穩(wěn)定性和穩(wěn)定的晶體結(jié)構(gòu),是理想的低脂低糖高纖食品加工原料,本研究結(jié)果可為椰肉加工副產(chǎn)物在食品工業(yè)中的高值化利用提供理論指導(dǎo)。
關(guān)鍵詞:椰粕;椰麩;營(yíng)養(yǎng)評(píng)價(jià);加工特性;食品原料中圖分類(lèi)號(hào):TS209""""""文獻(xiàn)標(biāo)志碼:A
Comparative"Analysis"of"Nutritional"and"Physicochemical"Properties"of"Coconut"Meat"Processing"By-products
LI"Jiaqi1,2,"PENG"Shaodan1,"HUANG"Xiaobing1*,"ZHOU"Wei1,"LI"Ruyi1,"CHEN"Mianhong1,"ZHANG"Li1,"DENG"Fuming3,"XU"Yongli4,"LI"Jihua1
1."Agricultural"Products"Processing"Research"Institute,"Chinese"Academy"of"Tropical"Agricultural"Sciences"/"Key"Laboratory"of"Tropical"Crop"Products"Processing,"Ministry"ofnbsp;Agriculture"and"Rural"Affairs,"Zhanjiang,"Guangdong"524001,"China;"2."College"of"Food"Science"and"Technology,"Huazhong"Agricultural"University,"Wuhan,"Hubei"430070,"China;"3."Coconut"Research"Institute,"Chinese"Academy"of"Tropical"Agricultural"Sciences,"Wenchang,"Hainan"571339,"China;"4."College"of"Tropical"Crops,"Yunnan"Agricultural"University,"Pu’er,"Yunnan"665099,"China
Abstract:"Coconut"oil"residue"(COR)"and"coconut"milk"residue"(CMR)"are"the"two"main"by-products"of"coconut"meat,"which"are"produced"during"the"processing"of"coconut"oil"and"coconut"milk,"respectively."In"order"to"explore"the"processing"suitability"of"the"two"by-products,"the"nutritional"and"physicochemical"properties"of"the"two"by-products"were"comprehensively"analyzed."The"results"showed"that"the"fat"content"of"COR"(19.37"g/100"g)"was"lower"than"that"of"CMR,"while"the"nutrients"such"as"protein"(11.32"g/100"g),"total"dietary"fiber"(63.92"g/100"g),"soluble"dietary"fiber"(4.42"g/"100"g),"polysaccharides"(25.67"mg/g),"flavonoids"(4.21"mg/g),"total"phenols"(1.15"mg/g)"and"other"active"ingredients"were"higher"than"those"of"CMR."The"hydrolyzed"amino"acids"of"COR"and"CMR"were"similar,"but"the"content"was"significantly"different,"which"was"94.955"mg/g"and"56.975"mg/g,"respectively."COR"showed"better"hydration"properties"than"CMR"at"different"temperatures,"but"the"fluidity"of"both"was"poor."COR"had"relatively"higher"thermal"stability,"more"complete"crystal"structure"and"higher"group"activity"than"CMR."In"conclusion,"compared"with"CMR,"COR"has"more"nutrients"and"active"ingredients,"hydration"properties"and"fluidity,"and"has"higher"thermal"stability"and"stable"crystal"structure,"which"is"an"ideal"raw"material"for"low-fat,"low-sugar"and"high-fiber"food"processing."The"results"of"this"study"could"provide"theoretical"guidance"for"the"high-value"utilization"of"coconut"meat"processing"by-products"in"the"food"industry.
Keywords:"coconut"oil"residue;"coconut"milk"residue;"nutritional"evaluation;"processing"characteristics;"food"raw"material
DOI:"10.3969/j.issn.1000-2561.2024.12.025
椰子(Cocos"nucifera"L.)是我國(guó)重要的木本油料作物和熱帶特色經(jīng)濟(jì)作物,主要分布于海南、廣東南部、云南南部及臺(tái)灣等地區(qū),其中海南省椰子種植面積約37"333"hm2,占全國(guó)的99%,年產(chǎn)量約2.2億個(gè),全產(chǎn)業(yè)鏈產(chǎn)值約200億元[1],是海南“六棵樹(shù)”之一,也是支撐我國(guó)熱帶地區(qū)鄉(xiāng)村振興的支柱產(chǎn)業(yè)。椰肉風(fēng)味獨(dú)特,營(yíng)養(yǎng)價(jià)值高,富含蛋白質(zhì)、脂肪、膳食纖維和鈣、磷、鉀等礦物質(zhì)[2],目前主要以榨汁、榨油、干制加工為主。據(jù)統(tǒng)計(jì),全球每年椰肉加工產(chǎn)生的副產(chǎn)物達(dá)6300萬(wàn)t[3],椰粕(coconut"oil"residue,"COR)和椰麩(coconut"milk"residue,"CMR)是產(chǎn)量最高的2種副產(chǎn)物,分別由椰肉榨油和榨奶干燥后得到。研究表明,椰肉加工副產(chǎn)物含有豐富的營(yíng)養(yǎng)成分,分別含有4.2%~12.6%的蛋白質(zhì)、9.2%~42.6%的脂肪、19.2%~39.1%的碳水化合物和超過(guò)20%的膳食纖維[4],具有良好的開(kāi)發(fā)利用價(jià)值。然而,由于加工理論與技術(shù)研究不足,椰肉加工副產(chǎn)物未得到合理的開(kāi)發(fā)與利用,目前工業(yè)上開(kāi)發(fā)利用模式主要停留在以生產(chǎn)動(dòng)物飼料[5-7]、纖維材料[8]、作物肥料[9-11]等低附加值產(chǎn)品階段,利用其營(yíng)養(yǎng)特性開(kāi)發(fā)高值化、功能化食品的相關(guān)研究較少。因此,為加快椰肉加工副產(chǎn)物在食品領(lǐng)域的開(kāi)發(fā)利用,本研究以椰肉2種主要加工副產(chǎn)物COR和CMR為研究對(duì)象,系統(tǒng)比較分析2種副產(chǎn)物的營(yíng)養(yǎng)特點(diǎn)與加工特性,以期為其食品化開(kāi)發(fā)利用提供理論依據(jù)與方法指導(dǎo)。
1.1""材料
1.1.1""材料與試劑""椰粕(椰干冷壓榨所得,餅狀)和椰麩(椰肉打漿過(guò)濾后干燥得到,粉狀)由中國(guó)熱帶農(nóng)業(yè)科學(xué)院椰子研究所提供;石油醚、苯酚、無(wú)水乙醇、氯化鈉、氫氧化鈉、乙酸分析純,購(gòu)自西隴科學(xué)股份有限公司;牛血清白蛋白、無(wú)水碳酸鈉分析純,購(gòu)自麥克林生化科技有限公司。
1.1.2""儀器與設(shè)備""1000Y型萬(wàn)能粉碎機(jī)購(gòu)自永康市鉑歐五金制品有限公司;Kjeltec?"8400全自動(dòng)凱氏定氮儀、Fibertec"2010全自動(dòng)纖維分析系統(tǒng)購(gòu)自丹麥FOSS公司;BT-1000型粉體綜合特性測(cè)試儀購(gòu)自丹東百特科技有限公司;Sigma/"3-30K低溫離心機(jī)購(gòu)自美國(guó)Sigma公司;A300型全自動(dòng)氨基酸分析儀購(gòu)自德國(guó)MembraPure公司;DF-06型膳食纖維測(cè)定儀購(gòu)自海能未來(lái)技術(shù)集團(tuán)股份有限公司;DSCQ2000差示掃描量熱儀購(gòu)自美國(guó)TA公司;INVENNIO"S型傅里葉變換紅外光譜儀購(gòu)自德國(guó)Bruker公司。
1.2""方法
1.2.1""樣品的制備""COR和CMR粉碎后過(guò)60目篩,密封保存?zhèn)溆谩?/p>
1.2.2""基礎(chǔ)營(yíng)養(yǎng)成分分析""水分含量參照GB"5009.3—2016《食品中水分的測(cè)定》第一法直接干燥法測(cè)定;粗蛋白含量參照GB"5009.5《食品安全國(guó)家標(biāo)準(zhǔn)"食品中蛋白質(zhì)的測(cè)定》中第一法凱氏定氮法測(cè)定;粗脂肪含量參照GB"5009.6《食品安全國(guó)家標(biāo)準(zhǔn)"食品中脂肪的測(cè)定》中第一法索氏抽提法測(cè)定;灰分含量參照GB"5009.4《食品安全國(guó)家標(biāo)準(zhǔn)"食品中灰分的測(cè)定》中第一法測(cè)定;粗纖維含量參照GB/T"5009.10—2003《植物類(lèi)食品中粗纖維的測(cè)定》測(cè)定。
1.2.3""還原糖含量測(cè)定""采用二硝基水楊酸比色法[12]測(cè)定樣品還原糖含量,葡萄糖標(biāo)準(zhǔn)曲線為y=1.791x?0.0616,R2=0.9996,據(jù)此計(jì)算樣品中的還原糖含量。
1.2.4""膳食纖維分析""采用DF06型膳食纖維測(cè)定儀測(cè)定可溶性膳食纖維(soluble"dietary"fiber,"SDF)、不溶性膳食纖維(insoluble"dietary"fiber,"IDF)以及總膳食纖維(total"dietary"diber,"TDF)含量。
1.2.5""組分蛋白測(cè)定""采用Osboren法[13]提取組分蛋白,Bradford法測(cè)定提取液中蛋白濃度,牛血清白蛋白標(biāo)準(zhǔn)曲線為y=0.816x+0.0368,R2="0.9974,據(jù)此計(jì)算各組分蛋白含量。
1.2.6""氨基酸組成分析""稱取0.50"g樣品于水解管中,加15"mL鹽酸溶液,于110"℃水解24"h,冷卻后抽濾,取濾液定容至25"mL,取2"mL吹干,加4"mL樣品稀釋液,漩渦震蕩使其溶解,過(guò)0.45"μm濾膜后加入進(jìn)樣瓶中,上機(jī)分析。
1.2.7""多糖含量測(cè)定""采用苯酚-硫酸法[14]測(cè)定樣品中的多糖含量,葡萄糖標(biāo)準(zhǔn)曲線為y=15.13x?"0.0107,R2=0.9988,據(jù)此計(jì)算樣品中的多糖含量。
1.2.8""黃酮含量測(cè)定""采用亞硝酸鈉-硝酸鋁比色法[15]測(cè)定樣品中的黃酮含量,蘆丁標(biāo)準(zhǔn)曲線為y=1.1386x?0.0082,R2=0.9992,樣品中的黃酮含量以蘆丁當(dāng)量(RTE)表示,據(jù)此計(jì)算樣品中的黃酮含量。
1.2.9""總酚含量測(cè)定""采用福林酚比色法[16]測(cè)定樣品中的總酚含量,沒(méi)食子酸標(biāo)準(zhǔn)曲線為y=8.7781x+0.0222,R2=0.9993,樣品中的多酚含量以沒(méi)食子酸當(dāng)量(GAE)表示,據(jù)此計(jì)算樣品中的多酚含量。
1.2.10""水溶性的測(cè)定""參考ANDERSON等[17]的方法并稍作修改,稱取2.0"g樣品,加入30"mL蒸餾水,漩渦振蕩使樣品完全分散于水中,分別于40、50、60、70、80、90"℃下保溫60"min,每隔15"min振蕩1次,過(guò)濾后將濾液轉(zhuǎn)移至燒杯中,105"℃烘干至恒重,計(jì)算樣品的水溶性指數(shù)。
1.2.11""溶脹性的測(cè)定""參考ZHANG[18]等的方法并稍作修改,稱取3.0"g樣品,倒入量筒,記錄體積,向量筒中加30"mL蒸餾水,混合均勻,靜置24"h,每隔3"h讀取1次自由膨脹體積,計(jì)算樣品的溶脹性。
1.2.12""持水性與持油性的測(cè)定""參考KEBEDE等[19]的方法并稍作修改,稱取0.2"g樣品分別與10"mL蒸餾水(油)充分混合,分別在40、50、60、70、80、90"℃下保持40"min,離心,棄上清液,計(jì)算樣品的持水性和持油性。
1.2.13""密度與壓縮度的測(cè)定""參考ABDULLAH等[20]的方法并稍作修改,將樣品裝于10"mL干燥潔凈的量筒內(nèi),填充至10"mL刻度處,稱量樣品和量筒質(zhì)量。再將裝有樣品的量筒在厚紗布上振實(shí)300次,至樣品體積無(wú)變化,讀取此時(shí)樣品的體積,分別計(jì)算堆積密度、振實(shí)密度和壓縮度。
1.2.14""休止角和滑角的測(cè)定""采用BT-1000型粉體綜合特性測(cè)試儀測(cè)定休止角和滑角。
1.2.15""掃描電鏡分析(SEM)""將導(dǎo)電膠貼到金屬試樣板上,沾取少量樣品,使其均勻地落在導(dǎo)電膠帶上,吹去未粘住的試樣。將粘有樣品的試樣板置于離子濺射儀試樣艙內(nèi),噴金,隨后在50倍和600倍下進(jìn)行觀察。
1.2.16""熱穩(wěn)定性分析(DSC)""稱取5"mg樣品置于鋁坩堝中,壓片機(jī)壓片,與空白坩堝一起放到儀器樣品架上進(jìn)行掃描。充入流量為50"mL/min的氮?dú)猓?0~250"℃的范圍內(nèi)以10"℃/min勻速升溫。
1.2.17""X-射線衍射分析(XRD)""將樣品放在載玻片上壓平,在管流為30"mA,管壓為30"kV,靶型為Cu的條件下進(jìn)行分析,以10°/min的掃描速度在5≦2θ≦90°的范圍內(nèi)對(duì)樣品進(jìn)行掃描,步長(zhǎng)為0.02°。利用Origin"軟件在5°≦2θ≦60°的范圍內(nèi)分別對(duì)結(jié)晶區(qū)和總衍射區(qū)進(jìn)行積分,用結(jié)晶區(qū)面積與總衍射區(qū)面積的比值來(lái)代表相對(duì)結(jié)晶度(relative"crystallinity,"RC)。
1.2.18""傅里葉紅外光譜分析(FT-IR)""稱取2"mg樣品與溴化鉀按1∶100的比例混合,研磨成均勻的粉末,烘干,壓片后測(cè)試,在4000~"400"cm?1之間的吸收模式下掃描FT-IR光譜,掃描次數(shù)為32次,分辨率為4"cm?1。
1.3""數(shù)據(jù)處理
試驗(yàn)結(jié)果均為至少3次重復(fù)試驗(yàn)的平均值,表示為均值±標(biāo)準(zhǔn)差,采用Excel"2021軟件進(jìn)行數(shù)據(jù)統(tǒng)計(jì)分析,采用Origin"2021軟件進(jìn)行顯著性分析及圖形繪制。
2.1""營(yíng)養(yǎng)成分分析
2.1.1""營(yíng)養(yǎng)成分與活性成分分析""COR和CMR的營(yíng)養(yǎng)成分與活性成分測(cè)定結(jié)果如表1所示,蛋白質(zhì)、脂肪和膳食纖維是二者的主要成分,COR的粗蛋白含量為11.32"g/100"g,是CMR的1.92倍,但二者的可溶性蛋白含量相當(dāng),分別為47.07、48.75"mg/g,谷蛋白是COR可溶性蛋白的主要組分,CMR則相反,主要組分蛋白為清蛋白和球蛋白,這與RODSAMRAN等[21]的研究結(jié)果一致;COR和CMR均含有較多的油脂,其中CMR的脂肪高達(dá)49.27"g/100g,接近全粉質(zhì)量一半,這些油脂賦予了原料特有的椰香,也具有一定的應(yīng)用前景;膳食纖維被譽(yù)為第七大營(yíng)養(yǎng)素,包括IDF和SDF,IDF可以促進(jìn)胃腸道蠕動(dòng),加快食物通過(guò)胃腸道,SDF能夠降低患心臟病、高血脂、糖尿病等慢性疾病的風(fēng)險(xiǎn)[22]。COR和CMR的膳食纖維含量分別為63.92"g/100g和38.33"g/100g,其中SDF分別為4.42"g/100g和1.98"g/100g,分別占比6.91%和5.17%,二者SDF含量均不高,在食品工業(yè)中可以通過(guò)改性拓展其利用值。
比較二者的活性成分發(fā)現(xiàn),COR的多糖、黃酮和總酚含量均高于CMR,一方面,這可能是因?yàn)镃MR含有較高的脂肪以及色素等脂溶性成分,使得活性成分被緊緊包裹在脂肪顆粒的內(nèi)部,不易被釋放到溶劑中,導(dǎo)致提取率降低[23]。另一方面,2種副產(chǎn)物的前加工工藝的不同也可能造成活性成分含量的差異,椰油為冷榨工藝,在一定程度上保護(hù)了活性成分,椰奶的制作工藝包括熱加工和機(jī)械打漿,在熱加工過(guò)程中會(huì)使椰肉中的水溶性多糖被帶至椰奶中,而劇烈的機(jī)械打漿也會(huì)造成黃酮和多酚損失。
2.1.2""水解氨基酸分析""如表2所示,COR和CMR均含有17種水解氨基酸,包括8種必需氨基酸和9種非必需氨基酸。COR的氨基酸總量為94.955"mg/g,其中必需氨基酸含量為28.625"mg/g,占比30.15%;CMR的氨基酸總量為56.975"mg/g,必需氨基酸含量為16.495"mg/g,占總量的28.95%。谷氨酸是椰肉加工副產(chǎn)物中含量最高的非必需氨基酸,亮氨酸、苯丙氨酸和纈氨酸是含量前三的必需氨基酸。此外,COR和CMR中還含有天冬氨酸、谷氨酸、甘氨酸等5種藥用氨基酸[24],分別占氨基酸總量的53.39%和48.73%。椰肉加工副產(chǎn)物水解氨基酸含量較高、種類(lèi)豐富,且氨基酸模式理想,在食品和藥品領(lǐng)域具有良好的開(kāi)發(fā)利用價(jià)值。
2.2""理化特性分析
2.2.1""水溶性分析""由圖1可知,隨著溫度的升高,COR和CMR的溶解率均呈現(xiàn)出先上升后降低的趨勢(shì),當(dāng)溫度達(dá)到70"℃時(shí),溶解率達(dá)到最大值。蛋白質(zhì)是影響樣品溶解度的主要物質(zhì),試驗(yàn)結(jié)果也側(cè)面反映了樣品中的蛋白質(zhì)在升溫過(guò)程中先解離而后又發(fā)生變性聚集,適當(dāng)升高溫度,可以使部分聚集態(tài)的蛋白解離,并促進(jìn)蛋白質(zhì)分子在水中的運(yùn)動(dòng),增強(qiáng)蛋白質(zhì)與水分子相互作用,從而提高樣品的溶解率。但當(dāng)環(huán)境溫度達(dá)到椰肉蛋白的變性起始溫度(70"℃左右)時(shí),部分蛋白質(zhì)發(fā)生變性,部分已經(jīng)解離的蛋白質(zhì)重新聚集,導(dǎo)致樣品的溶解度降低[25]。此外,在相同溫度下,COR的溶解率始終要強(qiáng)于CMR,這可能是COR中的蛋白質(zhì)、多糖、SDF等可溶性成分的含量要高于CMR,同時(shí)由于CMR由椰肉榨汁所得,殘留的油脂含量較高,且水溶性成分在其加工過(guò)程中流失也是其溶解率較低的原因之一。
2.2.2""溶脹性分析""圖2為室溫下COR和CMR的24"h溶脹曲線,隨著時(shí)間的延長(zhǎng),樣品的溶脹性逐漸上升而后趨于穩(wěn)定,且COR的溶脹性要優(yōu)于CMR。溶脹性主要取決于其中的SDF,隨樣品在水中浸泡時(shí)間的延長(zhǎng),SDF中的親水性基團(tuán)更多地露出,從而使其吸水伸長(zhǎng)后產(chǎn)生更大的體積,提高了樣品的溶脹性[26],而COR的SDF含量要顯著高于CMR,可能是COR溶脹性相對(duì)較高的主要原因。
2.2.3""持水性與持油性分析""由圖3可知,COR和CMR的持水性和持油性隨溫度的升高呈現(xiàn)先升后降的趨勢(shì),且相同溫度下COR的持水力和持油力均高于CMR。在70"℃附近,COR的持水性和持油性分別為9.92"g/g和5.33"g/g,CMR的持水性和持油性分別為8.43"g/g和4.73"g/g,均達(dá)到最大值。溫度超過(guò)70"℃后,樣品的持水性和持油性出現(xiàn)降低趨勢(shì),這可能是高溫導(dǎo)致樣品中的纖維基質(zhì)以其致密的多孔網(wǎng)狀結(jié)構(gòu)被破壞,使得滯留、吸附在其內(nèi)部空隙間的水分、油脂抵御離心力的能力減弱[27],此外,高溫還會(huì)使蛋白質(zhì)分子間發(fā)生絮凝聚集,也會(huì)使樣品的持水性和持油性降低[28]。
2.2.4""流動(dòng)性評(píng)價(jià)""采用密度、壓縮度、休止角和滑角等指標(biāo)對(duì)物料的流動(dòng)性進(jìn)行評(píng)價(jià),由表3可知,COR的堆積密度、振實(shí)密度顯著高于CMR,說(shuō)明COR的孔隙率大,較大的孔隙率有利于親水基與溶劑分子間的吸附溶解[29],這也是其水合特性優(yōu)于CMR的重要因素,且COR的振實(shí)密度與堆積密度的比值更接近于1,說(shuō)明其流動(dòng)性比CMR好;COR壓縮度、休止角和滑角均明顯低于CMR,說(shuō)明COR可壓縮性大,休止角越小流動(dòng)性越好,當(dāng)物料的休止角≤40°時(shí),說(shuō)明流動(dòng)性良好,二者的休止角均大于40°,說(shuō)明2種副產(chǎn)物的流動(dòng)性整體均較差,但COR的流動(dòng)性要優(yōu)于CMR,可能是CMR脂肪含量較高所導(dǎo)致。
2.3""結(jié)構(gòu)表征
2.3.1""SEM觀察""2種椰肉加工副產(chǎn)物的微觀結(jié)構(gòu)如圖4所示,COR和CMR的微觀結(jié)構(gòu)類(lèi)似,均呈不規(guī)則塊狀,且表面粗糙,存在較多的凸起、凹陷結(jié)構(gòu)。在50倍下觀察發(fā)現(xiàn),COR顆粒小且分布均勻,而CMR顆粒較大、分布不均勻,顆粒之間分布密集,存在一定范圍的團(tuán)聚現(xiàn)象。放大到600倍觀察發(fā)現(xiàn),COR的顆粒各結(jié)構(gòu)處的輪廓較為清晰,而CMR各結(jié)構(gòu)處的輪廓呈現(xiàn)出膠黏狀,這可能是因?yàn)镃MR高油脂含量所導(dǎo)致,高油脂導(dǎo)致顆粒之間的相互作用力增加,黏度增加,在一定程度上也解釋了2.2.4中CMR流動(dòng)性較COR差的現(xiàn)象。
2.3.2""DSC分析""COR和CMR的DSC曲線見(jiàn)圖5,在50~350"℃的范圍內(nèi),二者的DSC曲線的形狀大似相同,均在80~120"℃附近出現(xiàn)了明顯的吸熱峰,主要是由水分蒸發(fā)引起,CMR水分蒸發(fā)峰的焓值明顯小于COR,說(shuō)明CMR中的水分更易蒸發(fā),這是因?yàn)镃MR的持水性較COR更低,鎖水效果較差。在300"℃附近出現(xiàn)明顯放熱峰,是由纖維熱降解引起,在此溫度范圍內(nèi),COR和CMR中的木質(zhì)素、半纖維素等成分發(fā)生降解并放出熱量[30]。COR和CMR的纖維熱解峰溫度范圍并無(wú)明顯差異,說(shuō)明二者所含纖維的成分基本相同,但與COR相比,CMR中的纖維熱分解放出的熱量較少,表明CMR中的纖維分解程度較低,更難分解,這可能是CMR較高的油脂含量所導(dǎo)致,因?yàn)橛椭赏ㄟ^(guò)包裹作用來(lái)阻礙蛋白、纖維等大分子熱分解。
2.3.3""XRD分析""COR和CMR在5≦2θ≦90°的范圍內(nèi)的XRD圖譜如圖6所示,2種副產(chǎn)物均在16.08°和20.12°附近出現(xiàn)了較強(qiáng)的結(jié)晶衍射峰,COR在23.82°、25.32°和32.94°附近出現(xiàn)3個(gè)強(qiáng)度較弱的結(jié)晶衍射峰,但CMR在對(duì)應(yīng)位置的衍射峰強(qiáng)度極低,幾乎消失。2種副產(chǎn)物均出現(xiàn)了典型的天然纖維素I晶體結(jié)構(gòu)特征衍射峰,說(shuō)明COR和CMR的纖維晶體類(lèi)型均屬于纖維素I型[31],2種副產(chǎn)物的出峰位置、峰形并無(wú)明顯差異,說(shuō)明2種副產(chǎn)物存在著較為相近的結(jié)晶區(qū)結(jié)構(gòu)。此外,COR的相對(duì)結(jié)晶度為13.56%,顯著高于CMR,說(shuō)明COR的晶體結(jié)構(gòu)更為完整,熱穩(wěn)定性更好,但2.3.2的結(jié)果顯示CMR的熱穩(wěn)定性更好,這說(shuō)明油脂的包裹作用占主導(dǎo)。
2.3.4""FT-IR分析""從圖7可以看出,COR和CMR的紅外圖譜形狀基本相似,但特征峰的峰高和峰面積有所不同。其中,3550"cm?1附近的特征峰對(duì)應(yīng)纖維素和半纖維素中羥基的伸縮振動(dòng)[32],COR在3550"cm?1附近出現(xiàn)了1個(gè)吸收峰,而CMR在對(duì)應(yīng)位置未出現(xiàn)明顯吸收峰,說(shuō)明COR存在較多的羥基,解釋了COR水溶性和溶脹性高于CMR這一試驗(yàn)結(jié)果[33];2種副產(chǎn)物在2950~"2850"cm?1范圍內(nèi)存在2個(gè)峰,分別對(duì)應(yīng)蛋白質(zhì)和油脂的脂肪鏈中的-CH2和-CH3基團(tuán)的對(duì)稱和不對(duì)稱伸縮振動(dòng)[34],這是其高脂肪含量所導(dǎo)致;1747"cm?1附近的特征峰對(duì)應(yīng)酯羰基的拉伸振動(dòng),這是半纖維素的特征吸收峰[34-36];1152"cm?1附近的強(qiáng)吸收峰對(duì)應(yīng)糖苷鍵的伸縮振動(dòng)[37],COR對(duì)應(yīng)的特征峰數(shù)量和強(qiáng)度均高于CMR,可能是由于COR中的膳食纖維含量更高。
近年來(lái),在健康飲食的大背景下,椰汁、椰奶、椰油等椰子產(chǎn)品越來(lái)越受到消費(fèi)者的青睞,椰肉加工業(yè)進(jìn)入新的發(fā)展機(jī)遇期。隨著椰肉加工業(yè)的迅速發(fā)展,椰粕和椰麩等椰肉加工副產(chǎn)物的產(chǎn)量也在逐年增加。但目前椰子企業(yè)對(duì)椰粕、椰麩等副產(chǎn)物的利用率極低,大部分椰粕、椰麩在產(chǎn)生后會(huì)被直接丟棄,污染環(huán)境,僅有一小部分被回收利用,并且對(duì)其開(kāi)發(fā)利用仍停留在相對(duì)淺顯的層面,精深加工水平極低,國(guó)際市場(chǎng)上的相關(guān)產(chǎn)品還處于原輔料和半成品階段。加工理論與技術(shù)研究方面的不足是限制椰粕和椰麩的高值化利用及其食品配料研發(fā)的主要原因,現(xiàn)階段國(guó)內(nèi)外對(duì)椰肉加工副產(chǎn)物的研究主要是針對(duì)其中某一特定組分開(kāi)展,對(duì)副產(chǎn)物整體開(kāi)發(fā)利用方面的研究鮮有報(bào)道,無(wú)法為椰子企業(yè)在副產(chǎn)物回收利用方面提供理論支撐。為此,本研究對(duì)椰粕和椰麩2種最主要的椰肉加工副產(chǎn)物進(jìn)行了系統(tǒng)的營(yíng)養(yǎng)特性和理化特性分析,以期為其綜合利用提供理論與數(shù)據(jù)支撐。
對(duì)椰粕、椰麩營(yíng)養(yǎng)組成與理化特性的測(cè)定結(jié)果表明,與CMR相比,COR含有相對(duì)較低的脂肪(19.37"g/100"g)和較高的蛋白質(zhì)(11.32"g/100"g)、TDF(63.92"g/100"g)、SDF(4.42"g/100"g)、多糖(25.67"mg/g)、總黃酮(4.21"mg/g)、水解氨基酸(94.955"mg/g)含量,在低脂高纖食品配料方面更具備應(yīng)用前景。在水解氨基酸方面,COR與CMR中氨基酸種類(lèi)相似,均含有多種必需氨基酸和藥用氨基酸;同時(shí)COR具有相對(duì)較好的水合特性和流動(dòng)性,是一種易于加工的原料;此外,COR具有相對(duì)較高的熱穩(wěn)定性、較完整的晶體結(jié)構(gòu)。COR作為營(yíng)養(yǎng)相對(duì)豐富且低糖低脂高纖的天然原料,加工特性較好,來(lái)源廣泛、價(jià)格低廉、產(chǎn)地相對(duì)集中且產(chǎn)量較大,在食品工業(yè)中具有較大的開(kāi)發(fā)應(yīng)用潛力,本研究對(duì)椰肉加工副產(chǎn)物的食品化加工增值利用具有一定的指導(dǎo)意義。
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