周小理,杜麗娜,蔣晴怡,周一鳴
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超高壓處理改善苦蕎淀粉理化性質(zhì)及益生菌群落
周小理,杜麗娜,蔣晴怡,周一鳴※
(上海應(yīng)用技術(shù)大學(xué)香料香精技術(shù)與工程學(xué)院,上海 201418)
為研究超高壓(ultra-high pressure,HHP)處理對(duì)苦蕎淀粉理化性質(zhì)及功能性的影響,該文以6個(gè)不同壓力處理后的苦蕎淀粉為材料,利用掃描電鏡、X射線衍射儀等分析了其淀粉顆粒大小、晶體結(jié)構(gòu)、溶解度、透光率、凍融穩(wěn)定性等特性,并通過(guò)建立體外模型模擬人體消化以及腸道發(fā)酵過(guò)程,利用氣相色譜質(zhì)譜聯(lián)用技術(shù)和平板計(jì)數(shù)法,對(duì)小鼠糞便發(fā)酵液短鏈脂肪酸(short chain fatty acid、SCFAs)含量及主要菌群進(jìn)行了測(cè)定。試驗(yàn)結(jié)果表明:超高壓處理后苦蕎淀粉顆粒出現(xiàn)凹陷與粘連狀態(tài),并逐漸失去原有形態(tài),但其結(jié)晶類(lèi)型仍為典型的A型,其結(jié)晶度在200 MPa時(shí)達(dá)到最大值41.8%;溶解度和膨脹度均隨著壓力的增加呈先減小后增大的趨勢(shì),并且其透光率會(huì)下降,其中在200 MPa時(shí),溶解度和膨脹度都達(dá)到了最低0.83%和171%,而凍融穩(wěn)定性會(huì)有一定的改善。此外,超高壓處理后苦蕎淀粉使腸道中雙歧桿菌、乳酸桿菌的數(shù)量顯著增加(<0.05),而大腸桿菌、腸球菌的生長(zhǎng)受到顯著抑制(<0.05)。同時(shí),腸道內(nèi)的pH值顯著下降(<0.05)SCFAs中乙酸、丙酸、丁酸顯著增加(<0.05),綜上所述,超高壓處理后苦蕎可作為一種良好的天然改善腸道菌群的食物來(lái)源。
淀粉;發(fā)酵;高壓作用;苦蕎淀粉;體外發(fā)酵;SCFAs
苦蕎作為一種重要的農(nóng)作物,具有較高的營(yíng)養(yǎng)及藥用價(jià)值,其中所富含的蛋白質(zhì)(10%~18%)、淀粉(60%~70%)、纖維素(10%~16%)、脂肪(2%)以及黃酮類(lèi)化合物、B族維生素、礦物質(zhì)等營(yíng)養(yǎng)素[1-9]是其他農(nóng)作物無(wú)法比擬的。尤其是苦蕎中含有7%~10%的抗性淀粉[10],可降低腸道內(nèi)pH值改善腸道微生態(tài)[11],具有潛在益生作用。為此,國(guó)際谷物科技學(xué)會(huì)(international association for cereal science and technology,ICC)已將苦蕎作為一種新的潛在的頗具開(kāi)發(fā)前景的功能性食品配料。此外,苦蕎具有降血脂、降血糖,降低心血管疾病風(fēng)險(xiǎn)的功效[12],Hang等[13]用苦蕎全粉飼喂老齡大鼠發(fā)現(xiàn),苦蕎全粉能夠促進(jìn)大鼠腸道需氧菌和乳酸桿菌的數(shù)量的顯著增加(0.05),而使大腸桿菌和致病菌的數(shù)量小幅度減少;并且正常飼料和苦蕎全粉飼喂組大鼠腸道中都能檢出嗜酸乳桿菌、唾液乳酸桿菌、嬰兒雙歧桿菌,而植物乳桿菌、雙歧桿菌中的某些種只能在苦蕎飼喂組大鼠腸道內(nèi)容物中才能被檢出。
熱處理是食品加工過(guò)程中最常用的方法,不僅可以鈍化微生物,而且可以破壞酶。然而,某些極端條件下的熱加工處理會(huì)誘導(dǎo)若干化學(xué)和物理變化,從而破壞食品的感官性質(zhì)以及會(huì)降低某些生物活性化合物的含量及生物可利用性[14-15]。鑒于此,在食品生產(chǎn)中就需要有溫和的非熱加工技術(shù),例如:HHP、輻射、脈沖電場(chǎng)、超聲波以及振蕩磁場(chǎng)等,這些技術(shù)不僅可以獲得具有保持新鮮特色的高品質(zhì)的食品,而且可以提供功能得到改善的食品[16]。其中,隨著HHP等物理處理技術(shù)在食品工業(yè)的使用越來(lái)越廣泛,有關(guān)HHP對(duì)食品中營(yíng)養(yǎng)成分的影響成為近年來(lái)食品領(lǐng)域的研究熱點(diǎn)之一。與小分子營(yíng)養(yǎng)成分相比,大分子營(yíng)養(yǎng)成分在物理處理中的變化更為復(fù)雜,對(duì)食品(尤其是對(duì)于富含淀粉和蛋白質(zhì)的谷物食品)的品質(zhì)會(huì)產(chǎn)生重要的影響。
蕎麥淀粉近年來(lái)受到國(guó)內(nèi)外研究者的較多關(guān)注,國(guó)外關(guān)于苦蕎淀粉的研究已經(jīng)系統(tǒng)化,對(duì)苦蕎淀粉的生產(chǎn)、分析測(cè)定及其生理功能均做了廣泛研究[17]。特別是對(duì)于苦蕎淀粉可降低血清中膽固醇和甘油三酸酯水平等[18]這些方面已有了相對(duì)成熟的研究和進(jìn)展。但是對(duì)于苦蕎淀粉對(duì)人腸道菌群影響的研究相對(duì)較少。國(guó)內(nèi)關(guān)于苦蕎淀粉的研究尚還處于初級(jí)階段,對(duì)苦蕎淀粉的生產(chǎn)、分析和測(cè)定有一定的研究,但對(duì)于苦蕎淀粉在體內(nèi)的發(fā)酵和吸收研究較少,涉及到體外發(fā)酵試驗(yàn)內(nèi)容也不成熟。為此,本文通過(guò)建立體外模型模擬人體消化以及腸道發(fā)酵過(guò)程,研究HHP處理對(duì)苦蕎淀粉理化性質(zhì)以及小鼠腸道菌群的影響,從而為擴(kuò)大苦蕎產(chǎn)業(yè)化開(kāi)發(fā)和高值化的綜合利用提供科學(xué)依據(jù)。
苦蕎粉,山西雁門(mén)清高食品責(zé)任有限公司;苦蕎淀粉,實(shí)驗(yàn)室自提。
主要試劑:豬膽粉、豬膽鹽、L-半胱氨酸鹽、低聚果糖、維生素K1、氯化鐵血紅素、刃天青(均為分析純)購(gòu)自上海寶曼生物科技有限公司;MRS瓊脂培養(yǎng)基、BBL瓊脂培養(yǎng)基、伊紅美藍(lán)瓊脂培養(yǎng)基、腸球菌培養(yǎng)基購(gòu)自青島海博生物科技有限公司;氫氧化鈉、鹽酸、硫酸等常規(guī)試劑(均為分析純)等購(gòu)自國(guó)藥集團(tuán)(上海)化學(xué)試劑有限公司。
主要儀器設(shè)備:超高壓裝置(5L HPP 600 MPa)包頭科發(fā)高壓科技有限責(zé)任公司;X射線衍射儀(XRD-6000型)、氣相色譜質(zhì)譜儀(TQ8040)日本島津公司;掃描電子顯微鏡(JSM-6390型)日本電子株式會(huì)社;冷凍干燥機(jī)(FD-80型)北京博醫(yī)康實(shí)驗(yàn)儀器有限公司;超凈工作臺(tái)(SW-CJ-IBU)蘇凈集團(tuán)技術(shù)有限公司;厭氧培養(yǎng)箱(YQX-Ⅱ型)上海龍躍儀器設(shè)備有限公司;X射線衍射儀(XRD-6000型)、氣相色譜質(zhì)譜儀(TQ8040)日本島津公司;精密恒溫培養(yǎng)箱(BPH-9082型)上海一恒科學(xué)儀器有限公司;pH計(jì)(FE20型)梅特勒-托利多儀器(上海)有限公司。
1.2.1 苦蕎淀粉的制備
參照周小理等[16]的方法,制備苦蕎淀粉。
蕎麥、乙醇60 ℃水浴8 h,4 000 r/min,離心10 min得到沉淀物和水,調(diào)節(jié)pH值為10后浸提10 min再經(jīng)過(guò)4 000 r/min,離心10 min保留下層沉淀脫水、干燥得到蕎麥淀粉。
1.2.2 苦蕎淀粉超高壓處理
將苦蕎淀粉置于塑封袋中,放進(jìn)超高壓裝置,分別在常壓、100、200、300、400、500 MPa下處理,保壓15 min后,將樣品取出60 ℃烘干,粉碎研磨。處理后真空密封,放入干燥箱,備用。
1.2.3 苦蕎淀粉顆粒形態(tài)的測(cè)定
參照張玉榮等[19]的方法,對(duì)苦蕎淀粉顆粒形態(tài)進(jìn)行測(cè)定,放大倍數(shù)為1 500倍。
1.2.4 X射線衍射淀粉晶體
參照陳福泉等[20]的方法,對(duì)苦蕎蛋白結(jié)晶度進(jìn)行測(cè)定。
1.2.5 苦蕎淀粉溶解度和膨脹度的測(cè)定
參考He等[21-22]的方法,分別對(duì)苦蕎淀粉溶解度和膨脹度進(jìn)行測(cè)定。
1.2.6 苦蕎淀粉凍融穩(wěn)定性和凝沉穩(wěn)定性的測(cè)定
參考蒲華寅等[23]的方法,分別對(duì)苦蕎淀粉凍融穩(wěn)定性和凝沉穩(wěn)定性進(jìn)行測(cè)定。
1.2.7 苦蕎淀粉透光率的測(cè)定
參考劉文婷等[24]的方法,分別對(duì)苦蕎淀粉透光率進(jìn)行測(cè)定。
1.2.8 體外模型模擬人體消化過(guò)程
參照Fouhse等[25-26]的方法,建立體外模擬人體消化模型。
1.2.9 體外模型模擬腸道發(fā)酵過(guò)程
參照Ho等[27]的方法,建立體外模擬腸道發(fā)酵模型。采用逼迫法無(wú)菌收集小鼠糞便,取樣當(dāng)天換無(wú)菌墊料,減少外界微生物對(duì)樣品的污染。將每只小鼠糞便分別放入滅菌環(huán)氧樹(shù)脂管,立即用預(yù)還原的磷酸鹽緩沖液( 0.1mol/L, pH值7.0)按照 1:9比例稀釋。取10 mL 糞便稀釋液加入預(yù)還原基礎(chǔ)培養(yǎng)基中,樣品分為5個(gè)處理組,分別為陰性對(duì)照組(control check, CK)、低聚果糖組(陽(yáng)性對(duì)照組,fructo-oligosaccharides,F(xiàn)OS)、常壓組、200 MPa組、500 MPa組。將樣品加入混勻后在 37℃厭氧工作站中發(fā)酵,并在發(fā)酵的第0、8 、16 、32 h取樣檢測(cè)腸道菌群數(shù)量、pH值和短鏈脂肪酸。
1.2.10 苦蕎淀粉對(duì)腸道菌群的影響
采用平板涂布法進(jìn)行菌落計(jì)數(shù),選擇10-4、10-5、10-63個(gè)稀釋梯度進(jìn)行試驗(yàn)。稀釋液為1 mol/L 磷酸鹽緩沖溶液(phosphate buffer saline, PBS)(pH值為7.00)。取發(fā)酵液100L均勻涂布于不同的選擇培養(yǎng)基上。每個(gè)稀釋梯度做2個(gè)平行空白。
表1 細(xì)菌培養(yǎng)基種類(lèi)及其培養(yǎng)條件
1.2.11 短鏈脂肪酸及發(fā)酵液pH的測(cè)定
參照Gammacurta等[28]的方法,對(duì)短鏈脂肪酸及發(fā)酵液pH值進(jìn)行測(cè)定。
1.2.12 數(shù)據(jù)分析
每組試驗(yàn)重復(fù)3次,采用Excel軟件對(duì)試驗(yàn)數(shù)據(jù)進(jìn)行處理,并采用SPSS20.0對(duì)數(shù)據(jù)進(jìn)行因子方差分析及Duncan’s多重檢驗(yàn)(<0.05),試驗(yàn)結(jié)果以均值±標(biāo)準(zhǔn)差表示。
2.1.1 超高壓處理對(duì)苦蕎淀粉顆粒形態(tài)的影響
由圖1可知,HHP處理對(duì)于苦蕎淀粉的顆粒形態(tài)有明顯的影響,且隨著壓力的增加變化更為明顯,其中,在常壓下(如圖1a),苦蕎淀粉的顆粒多為卵圓形或多邊形,表面光滑,而經(jīng)過(guò)HHP處理15 min后,當(dāng)壓力條件在(100~300 MPa)時(shí)(如圖1b~1d),苦蕎淀粉表面開(kāi)始出現(xiàn)輕微裂紋,且表面較為粗糙;當(dāng)壓力達(dá)到400 MPa時(shí)(如圖1e),部分淀粉顆粒已明顯糊化、變形,且互相粘連,失去原有形態(tài);當(dāng)壓力達(dá)到500 MPa時(shí)(如圖1f),粘連和凹陷情況更加明顯,幾乎看不到完整的淀粉顆粒。這可能是由于淀粉顆粒在HHP處理時(shí),水分子受到壓力進(jìn)入淀粉顆粒內(nèi)部無(wú)定型區(qū)域以氫鍵形式優(yōu)先與水分子結(jié)合,無(wú)定型區(qū)域的吸水溶脹導(dǎo)致淀粉顆粒變大[29-30]。而且HHP處理會(huì)使支鏈淀粉和支鏈淀粉之間產(chǎn)生強(qiáng)烈的相互作用,導(dǎo)致光滑的淀粉表明產(chǎn)生空腔、裂縫和空洞。
圖1 不同超高壓壓力處理后苦蕎淀粉的掃描電子顯微鏡照片(1 500×)
2.1.2 不同超高壓處理對(duì)苦蕎淀粉顆粒晶體結(jié)構(gòu)的影響
由表2可知,苦蕎淀粉在衍射角2為14.64°,16.52°,17.63°、22.56°和28.64°時(shí)出現(xiàn)較強(qiáng)的特征衍射峰,屬于典型的A型粉的衍射圖譜。超高壓處理后(100~300 MPa),苦蕎淀粉的晶型結(jié)構(gòu)并未發(fā)生變化,但其衍射強(qiáng)度增加,且相對(duì)結(jié)晶度從35.0%增加到41.8%。這可能是由于苦蕎淀粉中直鏈淀粉含量為25.8%~32.6%,支鏈淀粉含量為52.13%~41.88%[31],支淀粉與支淀粉之間的交互作用,使得分子鏈上的羥基相互作用形成氫鍵,產(chǎn)生新的雙螺旋結(jié)構(gòu),形成新的結(jié)晶體。當(dāng)HHP處理壓力達(dá)到500 MPa時(shí),苦蕎淀粉X射線衍射圖譜在2為14.76°,16.56°,22.68°的3個(gè)強(qiáng)衍射峰發(fā)生合并,且各個(gè)衍射峰強(qiáng)度下降,結(jié)晶度降低,接近于0,說(shuō)明結(jié)晶結(jié)構(gòu)幾乎全部瓦解,形成完全的無(wú)定型淀粉,即500 MPa的HHP處理導(dǎo)致苦蕎淀粉發(fā)生糊化。
這一方面可能是由于A型淀粉構(gòu)成其晶體結(jié)構(gòu)的支鏈淀粉分子相對(duì)有較多的短支鏈,支鏈間形成的雙螺旋結(jié)構(gòu)較為松散,在壓力作用下很容易使原來(lái)的雙螺旋結(jié)構(gòu)破壞而形成新的螺旋結(jié)構(gòu),并導(dǎo)致晶體結(jié)構(gòu)的變化,進(jìn)而表現(xiàn)出晶型結(jié)構(gòu)的變化[32]。另一方面說(shuō)明A型淀粉不耐高壓,在較低的壓力條件下部分水分子就會(huì)進(jìn)入淀粉內(nèi)部,發(fā)生有限制的膨脹,從而使結(jié)晶區(qū)部分淀粉鏈雙螺旋結(jié)構(gòu)被解開(kāi),顆粒內(nèi)部結(jié)晶部分被破壞而減少。
表2 不同壓力處理后苦蕎淀粉顆粒晶型的分析
2.1.3 超高壓處理對(duì)苦蕎淀粉溶解性和膨脹度的影響
溶解度即淀粉乳的水合力,反映了淀粉顆粒的吸水性及其與水分子的結(jié)合程度。由于苦蕎淀粉的顆粒較小,比表面積大,苦蕎淀粉有較高的持水能力。圖2a、2b為不同HHP處理后苦蕎淀粉的溶解度和膨脹度,由圖2a和2b可知,HHP處理后的苦蕎淀粉溶解度和膨脹度均低于常壓條件下,結(jié)合圖1可知,這可能是由于經(jīng)過(guò)HHP處理的淀粉顆粒結(jié)構(gòu)發(fā)生了變化,淀粉顆粒之間相互聚集阻礙了水分進(jìn)入淀粉顆粒。并且,溶解度和膨脹度均隨著壓力的增加呈先減小后增大的趨勢(shì),其中在200 MPa時(shí),溶解度和膨脹度達(dá)到0.83%和171%,而當(dāng)壓力增加到300 MPa后又開(kāi)始逐漸升高,這與HHP處理后苦蕎淀粉析水率及凝沉穩(wěn)定性變化一致。
2.1.4 超高壓處理對(duì)淀粉透光率的影響
淀粉糊的透明度和老化程度關(guān)系密切,一般易老化的淀粉透明度較差。圖2c為不同HHP壓力處理前后苦蕎淀粉的透光率,由圖2c可知,經(jīng)HHP處理后的苦蕎淀粉透光率低于常壓下的苦蕎淀粉,且隨著壓力的增大而減小,這可能是由于HHP使淀粉晶體結(jié)構(gòu)受到破壞,壓力越大,晶體結(jié)構(gòu)破壞越嚴(yán)重。在壓力增大的過(guò)程中,沒(méi)有膨脹的淀粉顆粒和未完全破裂的淀粉顆粒的數(shù)量增多,導(dǎo)致光線發(fā)生散射,使淀粉的透光率下降。這主要與其淀粉顆粒的結(jié)晶度較高,糊化困難,導(dǎo)致淀粉糊中還存在沒(méi)有充分糊化的生淀粉有關(guān)。
圖2 超高壓處理對(duì)苦蕎淀粉顆粒性質(zhì)的影響
2.1.5 超高壓處理對(duì)苦蕎淀粉凍融穩(wěn)定性和凝沉穩(wěn)定性的影響
析水率的高低關(guān)系著凍融穩(wěn)定性的好壞,析水率越高,凍融穩(wěn)定性越差,而凍融穩(wěn)定性越差說(shuō)明淀粉乳形成的凝膠強(qiáng)度也較差,在加工、運(yùn)輸中意外的溫度波動(dòng)變化都會(huì)影響淀粉品質(zhì)。由圖2d可知,隨著壓力的增大,淀粉糊的析水率呈先下降后上升的趨勢(shì),其中,在200 MPa時(shí)達(dá)到最小值,當(dāng)壓力超過(guò)300 MPa時(shí)析水率又開(kāi)始上升。由此可知,適當(dāng)壓力的HHP處理(200 MPa)可降低淀粉糊的析水率,改善淀粉的凍融穩(wěn)定性,而隨著壓力的繼續(xù)增大,淀粉顆粒破壞較嚴(yán)重,析水率升高,淀粉品質(zhì)下降。
圖2e為不同HHP處理前后苦蕎淀粉的凝沉曲線。由圖2e可知,HHP處理后的苦蕎淀粉較常壓下苦蕎淀粉的沉降體積降低了10.9%~26.6%,其中,HHP處理(500 MPa)時(shí)苦蕎淀粉的沉降體積最小,且在300與500 MPa時(shí),淀粉凝膠保水能力較強(qiáng),200與400 MPa下次之,常壓和100 MPa下最差。
2.2.1 超高壓處理后苦蕎淀粉對(duì)雙歧桿菌數(shù)量的影響
雙歧桿菌在腸道菌群的平衡方面發(fā)揮重要作用,它能夠產(chǎn)生抑制非有益菌生長(zhǎng)的有機(jī)酸,并刺激腸道蠕動(dòng)。體外發(fā)酵過(guò)程中雙歧桿菌的數(shù)量變化見(jiàn)圖3a。由圖可知,在發(fā)酵前期(0~8 h),各組雙歧桿菌數(shù)量顯著增加(<0.05)。與空白組(未添加苦蕎淀粉)相比常壓組、HHP處理組(200 MPa)、HHP處理組(500 MPa)雙歧桿菌增加量依次為28.2%、37.0%和22.16%,說(shuō)明添加并經(jīng)適度HHP處理(200 MPa)后,苦蕎淀粉可以促進(jìn)雙歧桿菌增殖。這可能是由于經(jīng)過(guò)HHP處理后,苦蕎淀粉顆粒發(fā)生了不同程度的變化,淀粉顆粒表面積增加在一定程度上可提高雙歧桿菌對(duì)淀粉的利用率。這與Wronkowska等[33]研究結(jié)果一致。
2.2.2 超高壓處理后苦蕎淀粉對(duì)乳酸桿菌數(shù)量的影響
乳酸桿菌同樣可產(chǎn)生有機(jī)酸降低腸道pH值,從而抑制腐敗菌的增殖,維持腸道菌群的平衡。體外發(fā)酵過(guò)程中乳酸桿菌的數(shù)量變化見(jiàn)圖3b。由圖可知,在發(fā)酵前期(0~8 h),HHP處理組(200 MPa)乳酸桿菌增長(zhǎng)速率最高,增幅達(dá)到53.7%。其次是低聚果糖組,增長(zhǎng)率為37.0%。而HHP處理(500 MPa)組增幅只有19.5%,其原因可能是經(jīng)500 MPa HHP處理后淀粉中快消化淀粉、慢消化淀粉和抗消化淀粉比例發(fā)生變化,導(dǎo)致水解度下降,從而不容易被乳酸桿菌選擇性發(fā)酵。而在發(fā)酵中后期(8~32 h),低聚果糖組乳酸桿菌數(shù)量增幅達(dá)到70%以上,且HHP處理組中乳酸桿菌的增幅均小于常壓組。其原因可能是低聚果糖組中糖類(lèi)碳鏈較短,更便于乳酸桿菌利用,而苦蕎淀粉中的總糖碳鏈長(zhǎng),聚合度高,對(duì)腸道菌群的發(fā)酵作用有更高的抵抗力。在HHP處理后引起支鏈淀粉-支鏈淀粉間的相互作用,有助于形成一種致密的分子結(jié)構(gòu)從而影響乳酸桿菌利用。
2.2.3 超高壓處理后苦蕎淀粉對(duì)腸球菌數(shù)量的影響
腸球菌是人類(lèi)和動(dòng)物腸道正常菌群的一部分,近年研究己證實(shí)了腸球菌具有一定的致病性。體外發(fā)酵過(guò)程中腸球菌的數(shù)量變化見(jiàn)圖3c,由圖可知,發(fā)酵前期(0~8 h)腸球菌數(shù)量增加顯著(<0.05)。發(fā)酵中后期(8~32 h),除空白組外腸球菌數(shù)量均持續(xù)下降,其中HHP處理(500 MPa)組腸球菌下降幅度明顯,下降了8.9%,其次為低聚果糖組,下降了5.8%。相比于其他有害菌,腸球菌下降速度緩慢,推測(cè)腸球菌能夠在一定的酸性環(huán)境下存活生長(zhǎng),但不能長(zhǎng)時(shí)間在酸性環(huán)境下存在。
注:同一時(shí)間標(biāo)有不同小寫(xiě)字母表示有顯著差異(P<0.05),下同。
2.2.4 超高壓處理后苦蕎淀粉對(duì)大腸桿菌數(shù)量的影響
大腸桿菌為動(dòng)物或人腸道內(nèi)的條件致病菌,微生態(tài)平衡情況下是無(wú)害的,但一旦過(guò)量則會(huì)引起疾病。體外發(fā)酵過(guò)程中大腸桿菌的數(shù)量變化見(jiàn)圖3d,在發(fā)酵中后期(8~32 h),空白組大腸桿菌數(shù)量持續(xù)顯著上升(<0.05)。常壓、HHP處理(200 MPa)組、超高壓處理(500 MPa)組、低聚果糖組與空白組相比大腸桿菌數(shù)量分別下降了25.3%、5.24%、7.66%、40.0%。其原因可能是空白組中沒(méi)有抗性淀粉作為碳源,有益菌的生長(zhǎng)代謝受到抑制無(wú)法產(chǎn)生SCFAs而導(dǎo)致其發(fā)酵液pH值上升為大腸桿菌的生長(zhǎng)提供了有利環(huán)境。
圖4為HHP處理后苦蕎淀粉對(duì)SCFAs和發(fā)酵液pH值的影響,由圖4可知,相較于常壓組,HHP處理有利于短鏈脂肪酸的生成,其SCFAs濃度大小依次為:乙酸、丙酸、丁酸。其中,在發(fā)酵前期(0~8 h),HHP處理(200 MPa)組SCFAs濃度最高。即經(jīng)200 MPa處理后的苦蕎淀粉可有效降低腸道發(fā)酵液的pH值,抑制有害菌生長(zhǎng)。在發(fā)酵中后期(8~32 h),低聚果糖組SCFAs濃度最高。
乙酸是多數(shù)細(xì)菌發(fā)酵的主要代謝產(chǎn)物,能夠合成膽固醇,進(jìn)入人體參與物質(zhì)合成和代謝[32]。由圖4a可知,低聚果糖組、HHP處理(200 MPa)組和HHP處理(500 MPa)組乙酸含量顯著上升(<0.05),其中低聚果糖組在發(fā)酵過(guò)程中乙酸濃度最高,為6.63 mmol/L,其次是HHP處理(500 MPa)組,濃度為6.17 mmol/L。丙酸可以影響肝臟和膽固醇代謝[33-35],且丙酸的增加還能減弱肝膽固醇的合成[36],對(duì)人體結(jié)腸健康產(chǎn)生積極作用。由圖4b可知,低聚果糖組在發(fā)酵過(guò)程中丙酸濃度最高,為0.63 mmol/L,其次是HHP處理(200 MPa)組。丁酸在腸道中能提供能量,抑制腸癌細(xì)胞的生長(zhǎng)[37-38]。由圖4c可知,低聚果糖組在發(fā)酵過(guò)程中丁酸濃度最高,為0.59 mmol/L,其次是HHP處理(200 MPa)組,丁酸濃度為0.58 mmol/L。
從圖4d中可以得出,隨著發(fā)酵時(shí)間的增加,除空白組外,其余各組pH值均顯著下降(<0.05)。表明隨著發(fā)酵時(shí)間的增加,乳酸桿菌等腸道菌可以利用低聚果糖、苦蕎淀粉發(fā)酵產(chǎn)酸。其中,發(fā)酵8 h時(shí),常壓組pH值最低,為5.21。說(shuō)明在發(fā)酵前期(0~8 h)常壓苦蕎淀粉有利于腸道內(nèi)菌群利用產(chǎn)酸。發(fā)酵16 h時(shí),低聚果糖組pH值下降幅度最大,降幅達(dá)到55%,其次為HHP處理組(200 MPa)。發(fā)酵32 h時(shí),常壓組、HHP處理組(200 MPa)和HHP處理組(500 MPa)的pH值無(wú)顯著差異(>0.05)。綜上所述,在發(fā)酵中后期(8~32 h),除低聚果糖組外,HHP處理(200 MPa)的pH值下降幅度最大。這可能是由于HHP處理后,苦蕎淀粉中的顆粒發(fā)生變化,更有利于腸道菌群對(duì)其的利用。
圖4 超高壓處理后苦蕎淀粉對(duì)SCFAs、pH值的影響
本文比較系統(tǒng)分析了不同壓力處理后對(duì)苦蕎淀粉理化性質(zhì)的影響,并通過(guò)建立體外模擬胃腸道消化模型,分別對(duì)雙歧桿菌、乳酸桿菌、大腸桿菌以及腸球菌數(shù)量進(jìn)行分析。并通過(guò)氣相色譜質(zhì)譜聯(lián)用技術(shù),對(duì)體外模擬胃腸道消化發(fā)酵液中SCFAs含量及發(fā)酵液pH值進(jìn)行測(cè)定,研究結(jié)果表明:
1)HHP處理可以改變苦蕎淀粉顆粒結(jié)構(gòu)。當(dāng)壓力高于300 MPa時(shí),苦蕎淀粉顆粒表面會(huì)向內(nèi)凹陷,并逐漸被擠壓成塊狀或片狀并粘連在一起;且衍射強(qiáng)度逐漸增加(<0.05),相對(duì)結(jié)晶度從35.0%增加到41.8%,當(dāng)壓力達(dá)到500 MPa時(shí),苦蕎淀粉在500 MPa處理后的晶型特征由A型轉(zhuǎn)變?yōu)锽型。
2)HHP處理后,苦蕎淀粉的溶解度和膨脹度均小于常壓條件下;且經(jīng)適當(dāng)HHP處理(200 MPa)后,苦蕎淀粉析水率均低于常壓條件下,同時(shí),超高壓處理會(huì)降低苦蕎淀粉的透光率,并且隨著壓力和凝沉?xí)r間的增大,淀粉凝膠保水能力增強(qiáng)。
3)腸道微生物分析結(jié)果表明,適當(dāng)超高壓處理(200 MPa)的苦蕎淀粉具有一定的益生作用。其中,體外發(fā)酵前期(0~8 h),各組對(duì)小鼠腸道中雙歧桿菌及乳酸桿菌的選擇性增殖作用差異不大,大腸桿菌、腸球菌、數(shù)量均有一定增加。發(fā)酵中后期(8~32 h),除空白組外所有組益生作用明顯,均能夠被雙歧桿菌和乳酸桿菌利用,同時(shí)抑制大腸桿菌、腸球菌的增殖。
4)SCFAs主要是大腸內(nèi)碳水化合物發(fā)酵和蛋白質(zhì)降解的產(chǎn)物。腸道菌群通過(guò)產(chǎn)生SCFAs,改變腸道微生物群落,促進(jìn)腸道有益微生物繁殖,減少腐敗物和致癌物的產(chǎn)生、生成B族維生素、促進(jìn)腸道蠕動(dòng)、提高人體免疫力等。通過(guò)對(duì)小鼠糞便發(fā)酵液中SCFAs 含量以及pH值的測(cè)定發(fā)現(xiàn),除空白組外,其他各組pH值均呈現(xiàn)顯著下降(<0.05),SCFAs中乙酸、丙酸和丁酸均顯著增加。試驗(yàn)組與空白組相比SCFAs含量均有增加,并呈顯著性差異,表明苦蕎淀粉可能通過(guò)調(diào)節(jié)腸道菌群和腸道內(nèi)SCFAs 含量發(fā)揮益生元作用,也能在一定程度上為苦蕎對(duì)人體腸道產(chǎn)生的影響提供有效信息。
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Ultra-high pressure treatment improving physicochemical properties and probiotic community of tartary buckwheat starch
Zhou Xiaoli, Du Lina, Jiang Qingyi, Zhou Yiming※
(201418,)
With the improvement of people's living standards and health care awareness, diabetes, obesity, high blood pressure and other diseases increased year by year the issue has aroused people's attention. The key to solving these problems is to promote the use of high dietary fiber foods. Tartary buckwheat is rich in protein, starch, cellulose, flavonoids and other nutrients, it can improve intestinal microecology, lower blood lipids, prevent colon cancer, treat constipation and lose weight, it can also improve the immunity of human body. Starch, as the main component of tartary buckwheat, has high peak viscosity, high hydration capacity and low solubility. As a natural starch, it has shortcomings such as poor processing ability, narrow range of viscosity and unstable storage performance. Therefore, it needs to be modified to keep the functional characteristics of food to the maximum extent. In recent years, the physical modification method represented by ultra-high pressure, microwave, ultrasonic and other green processing technologies has been applied to starch modification, has become a focus recently. Compared with traditional heat treatment, it has a lower temperature of action. In this paper, the homemade tartary buckwheat starch was treated at 0.1 MPa (ordinary pressure), 100, 200, 300, 400, 500 MPa, and kept for 15 min, using scanning electron microscopy and X-ray diffractometry, etc. analyzed the characteristics of the morphology, crystal structure, solubility, light transmittance and freeze-thaw stability of the tartary buckwheat starch granules. The in vitro model was used to simulate human digestion and intestinal fermentation process. The contents of short chain fatty acids and the main bacterial flora of mouse fecal fermentation broth were determined. The experimental results show that when the pressure was higher than 300 MPa, the surface of tartary buckwheat starch would be inwardly depressed and gradually extruded into a block or sheet and adhered together; and the diffraction intensity was gradually increased (<0.05). The crystallinity increased from 35.0% to 41.8%. When the pressure reached 500 MPa, the crystal form of tartary buckwheat changed from A to B. Both solubility and expansibility decreased first and then increase with the increase of pressure, and the transmittance would go down, at 200 MPa, the solubility and expansion degree were both the lowest, and the freeze-thaw stability would be improved to some extent. In addition, in the pre-fermentation period (0-8 h), compared with the blank group (without added tartary buckwheat starch)the number ofandin the intestinal tract increased significantly after ultra-high pressure treatment (<0.05) , compared with the blank group (no tartary buckwheat starch was added), the increase ofin the ultra-high pressure treatment (200 MPa) group and the ultra-high pressure treatment (500 MPa) group was 37.0% and 22.16% respectively. Compared with the blank group, the growth rate ofincreased by 53.7% in the ultra-high pressure treatment (200 MPa) group, and the growth ofandwas significantly inhibited (<0.05). At the same time, the pH value in the intestine decreased significantly (<0.05). The acetic acid, propionic acid and butyric acid in SCFAs increased significantly (<0.05), among which, in the early stage of fermentation (0-8 h), the concentration of SCFAs in the ultra-high pressure treatment (200 MPa) group was the highest. That is, tartary buckwheat starch treated with 200 MPa could effectively reduce the pH value of intestinal fermentation fluid and inhibit the growth of harmful bacteria. In a word, after ultra-high pressure treatment, tartary buckwheat can be used as a good natural food for improving intestinal flora.
starch; fermentation; high pressure effects; tartary buckwheat starch; in vitro fermentation; SCFAs
10.11975/j.issn.1002-6819.2019.02.036
TS201
A
1002-6819(2019)-02-0284-09
2018-08-15
2018-12-17
國(guó)家自然科學(xué)基金面上基金項(xiàng)目(31871805);國(guó)家自然科學(xué)基金青年基金項(xiàng)目(31501437);國(guó)家現(xiàn)代農(nóng)業(yè)產(chǎn)業(yè)技術(shù)體系國(guó)家燕麥?zhǔn)w麥產(chǎn)業(yè)技術(shù)研發(fā)中心項(xiàng)目(CARS-07-E-2-03)
周小理,教授,研究方向?yàn)槭称沸沦Y源深度開(kāi)發(fā)與利用。Email:zhouxl@sit.edu.cn
周一鳴,副教授,博士,研究方向?yàn)楣δ苁称烽_(kāi)發(fā),食品加工與工藝。Email:zhouymsit@163.com
周小理,杜麗娜,蔣晴怡,周一鳴. 超高壓處理改善苦蕎淀粉理化性質(zhì)及益生菌群落[J]. 農(nóng)業(yè)工程學(xué)報(bào),2019,35(2):284-292. doi:10.11975/j.issn.1002-6819.2019.02.036 http://www.tcsae.org
Zhou Xiaoli, Du Lina, Jiang Qingyi, Zhou Yiming. Ultra-high pressure treatment improving physicochemical properties and probiotic community of tartary buckwheat starch[J]. Transactions of the Chinese Society of Agricultural Engineering (Transactions of the CSAE), 2019, 35(2): 284-292. (in Chinese with English abstract) doi:10.11975/j.issn.1002-6819.2019.02.036 http://www.tcsae.org