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(1.中國(guó)農(nóng)業(yè)科學(xué)院農(nóng)產(chǎn)品加工研究所農(nóng)業(yè)部農(nóng)產(chǎn)品質(zhì)量安全收貯運(yùn)管控重點(diǎn)實(shí)驗(yàn)室,北京 100193;2.中國(guó)農(nóng)業(yè)大學(xué)食品科學(xué)與營(yíng)養(yǎng)工程學(xué)院,國(guó)家果蔬加工工程技術(shù)研究中心,農(nóng)業(yè)部果蔬加工重點(diǎn)實(shí)驗(yàn)室,果蔬加工教育部工程研究中心,北京 100083;3.中國(guó)科學(xué)院理化技術(shù)研究所,北京 100190)

高壓均質(zhì)在液態(tài)食品殺菌中的研究進(jìn)展

劉偉1,宋弋2,廖小軍2,董鵬3,張潔1,林瓊1,吳杰1,王志東1,*

(1.中國(guó)農(nóng)業(yè)科學(xué)院農(nóng)產(chǎn)品加工研究所農(nóng)業(yè)部農(nóng)產(chǎn)品質(zhì)量安全收貯運(yùn)管控重點(diǎn)實(shí)驗(yàn)室,北京 100193;2.中國(guó)農(nóng)業(yè)大學(xué)食品科學(xué)與營(yíng)養(yǎng)工程學(xué)院,國(guó)家果蔬加工工程技術(shù)研究中心,農(nóng)業(yè)部果蔬加工重點(diǎn)實(shí)驗(yàn)室,果蔬加工教育部工程研究中心,北京 100083;3.中國(guó)科學(xué)院理化技術(shù)研究所,北京 100190)

高壓均質(zhì)是一種非熱加工技術(shù),隨著高壓技術(shù)和設(shè)備的發(fā)展和革新,現(xiàn)今高壓均質(zhì)的壓力可以達(dá)到400 MPa,為食品殺菌提供了新思路。相關(guān)研究認(rèn)為高壓均質(zhì)通過(guò)剪切、碰撞、空穴、湍流、渦旋、加熱等結(jié)合效應(yīng)對(duì)食品中的致病菌和腐敗微生物產(chǎn)生破壞作用。本文介紹了高壓均質(zhì)的作用原理,結(jié)合微生物、食品物料的理化特性、均質(zhì)條件等因素討論該技術(shù)在食品殺菌中的研究進(jìn)展,并分析了該技術(shù)的應(yīng)用前景。

高壓均質(zhì),超高壓均質(zhì),殺菌,微生物,芽孢

高壓均質(zhì)(High pressure homogenization,HPH)是一種非熱加工技術(shù),通過(guò)均質(zhì)機(jī)加工流體物料,減小物料粒徑,增加產(chǎn)品穩(wěn)定性,避免乳狀液分層、絮凝,主要應(yīng)用于食品、醫(yī)藥、生物、化工等領(lǐng)域[1]。傳統(tǒng)高壓均質(zhì)機(jī)的處理壓力一般為20～100 MPa,殺滅微生物的作用不顯著[2]。近年來(lái),隨著相關(guān)技術(shù)和設(shè)備革新,均質(zhì)機(jī)的壓力可以達(dá)到400 MPa,當(dāng)均質(zhì)壓力超過(guò)200 MPa時(shí),也被稱為超高壓均質(zhì)(Ultra high pressure homogenization,UHPH)。UHPH一方面可以使物料微粒大小達(dá)到納米級(jí),提高產(chǎn)品穩(wěn)定性;另一方面,UHPH還具有殺菌、鈍酶的作用,為流體食品殺菌提供了新的思路[3]。殺菌是食品加工過(guò)程中的重要操作單元。目前,食品工業(yè)中通常使用熱殺菌的方式加工食品,主要是以水或水蒸氣對(duì)食品進(jìn)行直接或間接的加熱、殺菌。但是,熱殺菌過(guò)程中的高溫作用很大程度上使食品的色澤、風(fēng)味、質(zhì)地和營(yíng)養(yǎng)成分發(fā)生改變或損失。而且,在耗能方面UHPH與超高溫瞬時(shí)處理(UHT,Ultra High Temperature treated)相比較具有較大優(yōu)勢(shì),一臺(tái)最大處理量達(dá)到20 L/h的UHT殺菌機(jī)的功率達(dá)到10 kW,而達(dá)到同樣處理量和殺菌效果的UHPH設(shè)備的功率僅為2.5 kW左右。隨著人們生活質(zhì)量和消費(fèi)水平的提高,安全、營(yíng)養(yǎng)、新鮮的食品日益受到市場(chǎng)的歡迎。近年來(lái),非熱殺菌技術(shù)成為食品工業(yè)領(lǐng)域中新的研究熱點(diǎn)。與傳統(tǒng)的熱殺菌技術(shù)相比,非熱殺菌過(guò)程中溫度相對(duì)較低,處理時(shí)間短,能夠更好地保持食品原有的品質(zhì)[2]。

1994年,Lanciotti等首次報(bào)道了HPH對(duì)于食品中致病菌和腐敗微生物的抑制作用,認(rèn)為HPH通過(guò)剪切、碰撞、空穴、湍流、渦旋、加熱等結(jié)合效應(yīng)對(duì)微生物產(chǎn)生破壞作用[4]。隨后,HPH在不同的模擬體系和牛乳制品、豆乳制品、蛋類食品、果蔬汁等食品體系展開進(jìn)一步的研究,結(jié)果表明HPH不僅能夠提高液體食品的穩(wěn)定性,較好的保持食品固有的營(yíng)養(yǎng)成分、色澤、香氣、延長(zhǎng)貨架期,又能夠在不同程度殺滅食品中的致病菌和腐敗微生物[5-9]。芽孢是某些處于生長(zhǎng)發(fā)育后期的細(xì)菌(芽孢桿菌、梭狀芽孢桿菌、少數(shù)球菌等)在逆境中產(chǎn)生的休眠體,芽孢在適宜環(huán)境下極易萌發(fā)成為營(yíng)養(yǎng)體造成食品二次污染,引發(fā)食品安全問(wèn)題。芽孢作為細(xì)菌的休眠體與細(xì)菌相比,對(duì)于高溫、低溫、輻射、干燥和化學(xué)物質(zhì)都有很強(qiáng)的抗性,研究發(fā)現(xiàn)HPH單獨(dú)處理,或結(jié)合其他物理、化學(xué)方法,可以不同程度地促進(jìn)萌發(fā)并殺滅孢子[7,10-13]。本文介紹了HPH作用原理和相關(guān)設(shè)備,結(jié)合微生物、食品物料的理化特性、均質(zhì)條件等因素討論HPH在食品殺菌的研究進(jìn)展,并分析了該技術(shù)的應(yīng)用前景。

1 HPH工作原理及設(shè)備介紹

早在1899年,Auguste Gaulin發(fā)明了均質(zhì)設(shè)備并應(yīng)用于牛奶加工,發(fā)現(xiàn)30 MPa均質(zhì)作用下可以提高牛奶的品質(zhì)[14]。從此,均質(zhì)技術(shù)應(yīng)用于提高乳制品以及其他乳狀液的穩(wěn)定性,改善產(chǎn)品品質(zhì)、風(fēng)味和貨架期[15]。隨著應(yīng)用領(lǐng)域的不斷擴(kuò)大,相關(guān)技術(shù)和設(shè)備的快速發(fā)展,均質(zhì)機(jī)的性能、規(guī)格有了很大的進(jìn)步,均質(zhì)壓力從30 MPa發(fā)展到100 MPa以上,現(xiàn)在已有可達(dá)到400 MPa的超高壓均質(zhì)機(jī),生產(chǎn)能力也發(fā)展到了數(shù)噸每小時(shí),而且均質(zhì)結(jié)構(gòu)多樣,包括:高壓(閥)均質(zhì)機(jī)、微射流儀、高壓(銳孔)均質(zhì)機(jī)等,使該技術(shù)廣泛的應(yīng)用在食品、醫(yī)藥、生物、化工、化妝品等行業(yè)中[16]。

高壓均質(zhì)機(jī)主要由高壓泵、均質(zhì)閥、傳動(dòng)裝置等構(gòu)成,高壓均質(zhì)機(jī)的工作原理如圖1所示,工作時(shí)由柱塞泵將液體物料以高壓低流速的狀態(tài)輸送至密閉的均質(zhì)閥區(qū),液體物料在高壓作用下迅速通過(guò)均質(zhì)閥中狹窄的間隙時(shí),物料的流速迅速地增加,而壓力也同樣地減低。物料同時(shí)受到高速剪切、高頻振蕩、空穴現(xiàn)象和對(duì)流撞擊等機(jī)械力作用和相應(yīng)的熱效應(yīng),可誘導(dǎo)物料大分子的物理、化學(xué)及結(jié)構(gòu)性質(zhì)發(fā)生改變,最終達(dá)到均質(zhì)的作用。HPH過(guò)程中,高壓均質(zhì)機(jī)首先被升高到設(shè)定的壓力,該過(guò)程導(dǎo)致系統(tǒng)內(nèi)部一定程度升溫(2～3 ℃/100 MPa),然后物料通過(guò)均質(zhì)閥,壓力降低,機(jī)械作用力轉(zhuǎn)化為熱能導(dǎo)致物料迅速升溫(14～18 ℃/100 MPa),整個(gè)HPH過(guò)程中物料升溫可達(dá)到16～22 ℃/100 MPa[17-20]。

圖1 高壓均質(zhì)工作原理Fig.1 Schematic diagram of working principle of high pressure homogenization

國(guó)內(nèi)外生產(chǎn)高壓均質(zhì)機(jī)的代表性公司包括:上海勵(lì)途機(jī)械設(shè)備工程有限公司、廣州聚能納米生物科技股份有限公司、上海東華高壓均質(zhì)機(jī)廠、河北廊坊通用機(jī)械制造有限公司、印度Goma公司、西班牙Ypsicon公司、美國(guó)BEE international公司、英國(guó)Stansted Fluid Power公司、德國(guó)Global Engineering Alliance公司等,生產(chǎn)的設(shè)備主要分為實(shí)驗(yàn)室均質(zhì)機(jī)和工業(yè)均質(zhì)機(jī)。實(shí)驗(yàn)室均質(zhì)機(jī)體積小而緊湊,可用于測(cè)試產(chǎn)品的均質(zhì)化效果并評(píng)估出最佳工藝參數(shù),一般最高均質(zhì)壓力為100～200 MPa,單位時(shí)間處理量為50～100 L/h。工業(yè)均質(zhì)機(jī)由壓縮模塊和均質(zhì)閥組成,前者可以通過(guò)高壓泵送產(chǎn)品,后者可以根據(jù)產(chǎn)品特點(diǎn)與所需結(jié)果將分散顆粒微?；癁槲⒚准?jí)或納米級(jí),一般最高均質(zhì)壓力為10～150 MPa,單位時(shí)間處理量為30～60000 L/h。進(jìn)口設(shè)備與國(guó)產(chǎn)設(shè)備相比較具有均質(zhì)壓力高、處理量大、性能穩(wěn)定、自動(dòng)化、連續(xù)化生產(chǎn)等優(yōu)勢(shì)[20]。Ypsicon公司開發(fā)了一體化的超高壓均質(zhì)滅菌設(shè)備,通過(guò)自動(dòng)化模塊將均質(zhì)機(jī)與熱交換器、冷卻設(shè)備以及無(wú)菌包裝設(shè)備整合在一起。處理過(guò)程中,物料預(yù)熱到90 ℃,處理壓力可以達(dá)到350 MPa,處理時(shí)間僅為0.2 s[2]。Gea Niro Soavi公司開發(fā)的ATENA系列中試均質(zhì)機(jī),在400 MPa工作壓力下平均流速為5 L/h[22]。高壓均質(zhì)機(jī)的作用壓力主要與均質(zhì)閥的結(jié)構(gòu)和材質(zhì)相關(guān),通過(guò)減小均質(zhì)閥的空隙可以提高均質(zhì)機(jī)的壓力,采用合金或陶瓷材料可以提高均質(zhì)閥的耐腐性和抗壓性[23]。當(dāng)均質(zhì)閥的孔隙為2～5 μm,均質(zhì)機(jī)的壓力可以達(dá)到400 MPa,為實(shí)現(xiàn)流體食品達(dá)到商業(yè)化滅菌提供了新的可能[22,24-25]。

2 HPH殺菌研究

表1 高壓均質(zhì)在模擬體系和食品體系中的殺菌作用匯總Table 1 Summary of HPH/UHPH microbial inactivation in relation to the model system and food system

注:-表示未報(bào)溫度;ND表示未檢測(cè)到微生物。

表1對(duì)HPH在模擬食品體系和食品體系中殺菌作用的研究進(jìn)展進(jìn)行了匯總。模擬食品體系主要包括水包油型乳液體系、油包水型乳液體系、培養(yǎng)基體系、PBS緩沖液體系等[4-5,7,38-40],食品體系包括牛奶、豆奶、蛋制品、果蔬汁等[5,19,32,40-43],研究表明HPH的殺菌作用主要受到微生物、均質(zhì)設(shè)備、均質(zhì)條件、物料體系等因素的影響。

2.1 微生物種類和初始濃度對(duì)HPH殺菌效果的影響

HPH的殺菌作用受到微生物種類和初始濃度影響,研究主要包括革蘭氏陽(yáng)性細(xì)菌、革蘭氏陰性細(xì)菌、霉菌和酵母菌[1,44]。Wuytack等研究了物料入口溫度為25 ℃均質(zhì)壓力為100～300 MPa對(duì)于五種革蘭氏陽(yáng)性細(xì)菌(Enterococcusfaecalis糞腸球菌,Staphylococcusaureus金黃色釀膿葡萄球菌,Lactobacillusplantarum胚牙乳桿菌,Listeriainnocua英諾克李斯特氏菌和Leuconostocdextranicum葡萄聚糖明串珠菌)和六種革蘭氏陰性細(xì)菌(Salmonellaentericaserovartyphimurium鼠傷寒沙門氏菌,Shigellaflexneri痢疾志賀氏菌,Yersiniaenterocolitica小腸結(jié)腸炎耶爾森菌,Pseudomonasfluorescens熒光假單胞菌和Escherichiacoli大腸桿菌)的作用,結(jié)果表明革蘭氏陰性細(xì)菌比革蘭氏陽(yáng)性細(xì)菌更容易被殺滅[7]。同樣,Pathanibul等發(fā)現(xiàn)在同一物料體系(蘋果汁和胡蘿卜汁)、初始菌落總數(shù)(5.8 log10CFU/mL)和物料入口溫度(25 ℃)條件下,物料中的E.coli經(jīng)過(guò)250 MPa處理減少了5 log10CFU/mL,而L.innocua需要350 MPa處理才能獲得相同的殺菌效果[43]。原因可能是革蘭氏陰性菌對(duì)于均質(zhì)壓力更為敏感,抗壓性更小。革蘭氏陽(yáng)性菌的細(xì)胞壁由多層肽聚糖組成,厚度為20～80 nm,而革蘭氏陰性菌細(xì)胞壁肽聚糖層厚度僅為1～7 nm。霉菌和酵母菌的抗壓性介于革蘭氏陽(yáng)性細(xì)菌和革蘭氏陰性細(xì)菌之間,可能是由于細(xì)胞體積較大以及細(xì)胞壁結(jié)構(gòu)的差異造成的結(jié)果。Tahiri等發(fā)現(xiàn)物料入口溫度25 ℃、200 MPa均質(zhì)5次使橙汁中的革蘭氏陰性菌E.coliO157∶H7降低了6log10CFU/mL,革蘭氏陽(yáng)性菌L.plantarum和Leuconostocmesenteroides分別降低了2.5和1.6 log10CFU/mL,酵母菌和青霉菌分別降低了2.3和4.0 log10CFU/mL[33]。研究表明HPH的殺菌效果與微生物的初始濃度有關(guān)。Tahiri等研究發(fā)現(xiàn)L.plantarum在磷酸鹽緩沖液(PBS)中的初始濃度為6 log10CFU/mL時(shí),物料入口溫度為25 ℃,經(jīng)過(guò)200 MPa處理5次后微生物可以完全被殺滅,而初始菌濃度為1 log10CFU/mL時(shí),相同的處理?xiàng)l件下僅殺滅小于1 log10CFU/mL。原因可能是隨著微生物初始濃度提高,其抗壓性在HPH過(guò)程中的也隨之增加[33]。也有研究表明HPH殺菌效果與微生物的初始濃度沒有顯著關(guān)系,Diels等發(fā)現(xiàn)E.coli在PBS緩沖液中的初始濃度為5～8 log10CFU/mL時(shí),在物料入口溫度為25 ℃,250 MPa處理都可以減少4 log10CFU/mL[40]。

2.2 工藝參數(shù)對(duì)HPH殺菌效果的影響

HPH的殺菌效果與均質(zhì)壓力、物料入口溫度、均質(zhì)閥溫度、均質(zhì)次數(shù)和均質(zhì)閥縫隙尺寸也有關(guān)系。一般而言,隨著處理均質(zhì)壓力、物料入口溫度和均質(zhì)次數(shù)的增加,HPH殺菌效果逐漸增強(qiáng)。Cruz等發(fā)現(xiàn)豆乳中的微生物自然菌群經(jīng)過(guò)物料入口溫度為40 ℃,200 MPa處理可以減少2.42 log10CFU/mL,而經(jīng)過(guò)300 MPa處理后可以減少4.24 log10CFU/mL[45]。同樣,Calligaris等發(fā)現(xiàn)香蕉汁中的微生物自然菌群經(jīng)過(guò)物料入口溫度為46.2 ℃,150 MPa處理可以減少1 log10CFU/mL,而處理壓力超過(guò)200 MPa時(shí)可以殺滅4 log10CFU/mL。物料入口溫度和均質(zhì)閥溫度對(duì)于HPH殺菌效果也有影響[27]。Ann等發(fā)現(xiàn)當(dāng)物料入口溫度低于35 ℃,均質(zhì)壓力達(dá)到300 MPa對(duì)于PBS緩沖液中的S.aureus沒有顯著作用,而當(dāng)入口溫度升高到50 ℃時(shí),同樣壓力下可以減少3 log10CFU/mL。杏仁飲料中的微生物自然菌群在物料入口溫度為 65 ℃,經(jīng)過(guò)200 MPa均質(zhì)可以減少1.69 log10CFU/mL;而當(dāng)物料入口溫度升高到75 ℃,同樣壓力下微生物自然菌群可以被完全殺滅[39]。Francesco等研究了SFP GEN 7400型均質(zhì)機(jī)和Bi NanoDeBee 45型均質(zhì)機(jī)對(duì)無(wú)菌水中的L.delbrueckii,S.cerevisiae和E.coli殺菌作用,發(fā)現(xiàn)隨著處理次數(shù)的增加,高壓均質(zhì)處理的殺菌效果逐漸增強(qiáng),GEN 7400型設(shè)備殺菌效果比NanoDeBee 45型更強(qiáng),可能是由于GEN 7400型設(shè)備的均質(zhì)閥孔隙較小,只有3～14 μm,而 NanoDeBee 45型設(shè)備的均質(zhì)閥孔隙較大,約為130 μm[46]。

另外,通過(guò)建立數(shù)學(xué)模型可以預(yù)測(cè)HPH的殺菌效果,有助于食品工業(yè)上HACCP中微生物安全性的控制,對(duì)優(yōu)化食品生產(chǎn)工藝也有一定的參考作用[47]。目前,高壓均質(zhì)處理過(guò)程中微生物殺菌模型的報(bào)道較少。Donsì等研究了物料入口溫度為2 ℃時(shí)不同壓力下高壓均質(zhì)處理對(duì)LactobacillusDelbrueckii德氏乳酸桿菌的殺菌效果,并將數(shù)據(jù)進(jìn)行一級(jí)反應(yīng)動(dòng)力學(xué)模型(線性模型)擬合[48]。另有研究考慮到均質(zhì)的處理次數(shù),以處理次數(shù)和均質(zhì)壓力為變量,使用 Weibull 模型(非線性模型)對(duì)殺菌數(shù)據(jù)進(jìn)行擬合[46-47]。以上兩種模型是研究在確定溫度下高壓均質(zhì)壓力(和處理次數(shù))對(duì)微生物殺菌效果的影響。董鵬研究了高壓均質(zhì)處理對(duì)S.aureus和E.coli殺菌效果的影響,以溫度和壓力為變量,利用二次多項(xiàng)式方程對(duì)殺菌結(jié)果進(jìn)行擬合。所用擬合方程為 log10(N/N0)=a+bT+cT2+dP+eP2+fTP,對(duì)所得擬合方程進(jìn)行分析,采用后向回歸法,逐步篩除方程中不顯著相關(guān)的變量,直至所有的變量都顯著相關(guān)[2]。

2.3 食品成分對(duì)HPH殺菌效果的影響

不同食品的組成成分對(duì)HPH殺菌也有影響。Ann等研究了HPH對(duì)于含有不同濃度聚乙二醇的PBS緩沖液中E.coli的殺菌作用,發(fā)現(xiàn)隨著聚乙二醇的濃度增加,PBS緩沖液的粘度逐漸增加,HPH對(duì)E.coli的殺菌作用逐漸減弱。當(dāng)壓力從100 MPa增加到300 MPa 時(shí),PBS緩沖溶液的相對(duì)黏度值從1.0升高到4.9時(shí),高壓均質(zhì)處理的殺菌效果從5.0 降低到2.9 log10CFU/mL[40]。Roig-Sagués等研究了HPH(200～400 MPa)對(duì)于含有不同濃度脂肪(0.3%～15%)的牛乳中L.monocytogenesCCUG 15526的殺菌效果,發(fā)現(xiàn)同樣壓力下,隨著脂肪含量的增加,殺菌效果越好。這可能是由于脂肪含量的升高導(dǎo)致了高壓均質(zhì)處理過(guò)程中均質(zhì)閥溫度的升高,從而增強(qiáng)了殺菌效果[42]。而Vachon等比較了HPH對(duì)PBS緩沖液和牛奶中L.monocytogenes和E.coli的殺菌作用,結(jié)果表明HPH對(duì)PBS緩沖液中L.monocytogenes和E.coli的殺菌效果更好,說(shuō)明脂肪在HPH過(guò)程中對(duì)微生物有一定的保護(hù)作用[25]。最后,通過(guò)向食品體系中添加抑菌成分可以提高HPH的殺菌作用。Matthew等發(fā)現(xiàn)乳酸鏈球菌素(Nisin)可以增強(qiáng)HPH對(duì)無(wú)菌生理鹽水中E.coli的殺菌效果[49]。而Pathanibul等發(fā)現(xiàn)Nisin(10 IU)對(duì)于HPH處理過(guò)程中蘋果汁和胡蘿卜汁中的 E. coli 殺菌沒有顯著作用,但是Nisin增強(qiáng)了HPH對(duì)L.innocua的殺菌效果,250 MPa均質(zhì)可以減少5 log10CFU/mL[43]。Kumar等發(fā)現(xiàn)殼聚糖可以增強(qiáng)HPH對(duì)蘋果汁中E.coli的殺菌效果[50]。另外,研究發(fā)現(xiàn)HPH可以通過(guò)改性作用使蛋白的疏水區(qū)域暴露,提高溶菌酶、過(guò)氧化物酶和乳鐵蛋白的抗菌活性,增加HPH對(duì)于壓力抗性較強(qiáng)的微生物如L.monocytogenes的殺菌作用[31,51-52]。目前,研究普遍認(rèn)為HPH過(guò)程中的伸應(yīng)力、撞擊、剪切和湍流等機(jī)械應(yīng)力和溫度升高是殺滅微生物的主要原因,但是具體的作用機(jī)制有待進(jìn)一步研究。Kumar等發(fā)現(xiàn)當(dāng)均質(zhì)壓力低于200 MPa時(shí),機(jī)械應(yīng)力是HPH殺滅蘋果汁中E.coli的主要原因;當(dāng)壓力超過(guò)250 MPa時(shí),較高的溫度是HPH殺菌的主要原因,此時(shí)均質(zhì)閥溫度高于70 ℃[50]。Dumay等認(rèn)為均質(zhì)閥溫度(Tvalve)在HPH殺菌過(guò)程中起到重要作用,當(dāng)Tvalve<60 ℃時(shí)HPH的殺菌作用主要?dú)w因于機(jī)械應(yīng)力,而當(dāng)Tvalve>60 ℃時(shí)HPH的殺菌作用主要?dú)w因較高的溫度[20]。

3.HPH對(duì)芽孢的殺滅作用

注:-表示未報(bào)溫度;ND表示未檢測(cè)到微生物。

表2對(duì)HPH在模擬食品體系和食品體系中殺滅孢子作用的研究進(jìn)展進(jìn)行了匯總。模擬食品體系主要包括水包油型乳液體系、雙蒸餾水、培養(yǎng)基體系、PBS緩沖液等[2,10,12,54],食品體系包括豆奶、牛奶、杏仁奶、冰激凌、蘋果汁、橙汁、植物飲料等[2,11,34-35,37,45,55-62]。研究表明HPH對(duì)于孢子的殺滅作用主要受到孢子種類、均質(zhì)設(shè)備、均質(zhì)條件、物料體系等因素的影響。部分研究發(fā)現(xiàn)HPH單獨(dú)處理,或結(jié)合其他物理、化學(xué)方法,可以不同程度地殺滅模擬食品體系和食品體系中部分芽孢[24,63-66]。同時(shí),另一部分研究表明在均質(zhì)壓力100～300 MPa,均質(zhì)閥溫度80～150 ℃條件下HPH對(duì)于殺滅芽孢無(wú)顯著作用。

3.1 芽孢種類對(duì)HPH殺滅芽孢的影響

芽孢的結(jié)構(gòu)與微生物營(yíng)養(yǎng)體有很大差別,主要由核心、皮層、芽孢衣、孢外壁等組成,一般認(rèn)為芽孢的強(qiáng)抗性與其緊密的內(nèi)部結(jié)構(gòu)、高度礦化的內(nèi)核和低含水率相關(guān)。能夠產(chǎn)生芽孢的細(xì)菌主要是革蘭氏陽(yáng)性菌中好氧性的芽孢桿菌屬(Bacillus)和厭氧性的梭菌屬(Clostridium),根據(jù)菌屬的不同芽孢的耐熱性也不同,有的甚至能耐受100 ℃及以上的高溫。從殺滅芽孢的角度講,均質(zhì)壓力需要與較高的溫度結(jié)合才能有較好的殺滅效果[55]。因此,芽孢的耐熱性對(duì)于HPH有顯著影響。Pereda等研究表明,牛奶中經(jīng)過(guò)300 MPa,均質(zhì)閥溫度為103 ℃處理后,其中自然存在的芽孢從1.7降低到0.6 log10CFU/mL[34]。對(duì)于耐高溫的G.stearothermophilusATCC 7953以及C.sporogenesPA 3679,兩者被接種到脫脂牛奶中,經(jīng)過(guò)300 MPa,物料入口溫度為45 ℃的高壓均質(zhì)處理16次以后,芽孢數(shù)量?jī)H僅降低了 0.67 log 10 CFU/mL[55]。

3.2 工藝參數(shù)對(duì)HPH殺滅芽孢的影響

基于高壓均質(zhì)機(jī)所能達(dá)到的工作條件,早期的研究集中在較低的均質(zhì)壓力(<200 MPa)和溫度(<50 ℃),結(jié)果表明HPH殺菌的效果并不理想。Feijoo等發(fā)現(xiàn)物料入口溫度為 50 ℃,200 MPa均質(zhì)冰淇淋中的B.licheniformisATCC 14580,芽孢的數(shù)量從4.30 log10CFU/mL僅僅減少了 0.55 log10CFU/mL[53]。隨著均質(zhì)技術(shù)和設(shè)備升級(jí),HPH在不同食品物料中表現(xiàn)出較好的殺滅芽孢的效果。Georget等發(fā)現(xiàn)PBS緩沖液中B.subtilisPS 832和G.stearothermophilusATCC 7953均質(zhì)閥溫度為145 ℃經(jīng)過(guò)300 MPa均質(zhì)后,芽孢數(shù)量分別減少了5和2 log10CFU/mL,物料通過(guò)均質(zhì)閥的時(shí)間小于0.5 s,較高的均質(zhì)閥溫度被認(rèn)為在殺滅芽孢中起到了主要作用[65]。Espejo等發(fā)現(xiàn)在物料入口溫度為75和85 ℃經(jīng)過(guò)300 Mpa均質(zhì)全脂牛奶中B.subtilis,B.cereus,B.licheniformis,B.sporothermodurans,B.coagulans和G.stearothermophilus的數(shù)量可以降低 5 log10CFU/mL[56]。但是,也有研究表明HPH對(duì)于殺滅牛奶中芽孢的作用并不顯著,Pereda等發(fā)現(xiàn)均質(zhì)閥溫度為 103 ℃ 經(jīng)過(guò)300 MPa均質(zhì)牛奶,其中自然存在的芽孢數(shù)量從 1.7 log10CFU/mL降低到0.6 log10CFU/mL[34]。Pinho等研究了HPH對(duì)于脫脂乳中ClostridiumsporogenesPA 3679孢子的抑制作用,結(jié)果表明在均質(zhì)閥84 ℃經(jīng)過(guò)300 MPa作用下使芽孢的數(shù)量芽孢數(shù)量從5 log10CFU/mL 僅減少了0.67 log10CFU/mL,而且沒有引起孢子對(duì)于熱抗性的改變[55]。因此,HPH達(dá)到牛奶產(chǎn)品商業(yè)無(wú)菌的要求還有待進(jìn)一步的研究。

另外,研究人員也比較了HPH和不同條件結(jié)合對(duì)于殺滅芽孢的作用,包括:低pH[10]、二甲基二碳酸鹽[12]、苯甲酸鈉等[11]。結(jié)果表明這些處理都不能有效提高HPH殺滅芽孢的作用。芽孢核中的吡啶二羧酸(Dipicolinic acid,DPA)和鈣離子(Ca2+)螯合 形 成 的 CaDPA,高含量的CaDPA可以保護(hù)芽孢。Chaves-López等發(fā)現(xiàn)B.cereus比B.subtilis對(duì)于熱處理更加敏感,150 MPa單獨(dú)處理可以使B.cereusSV 3中的DPA釋放量達(dá)到28.3%±4.0%,說(shuō)明HPH可以破壞芽孢的外部結(jié)構(gòu)。而HPH結(jié)合非等溫?zé)崽幚?32～85 ℃)可以使芽孢中DPA的釋放量達(dá)到46.8±4.3%,可能是HPH處理導(dǎo)致芽孢的抗熱性減弱,說(shuō)明HPH結(jié)合熱處理可以有效提高殺滅芽孢的作用[54]。

4 總結(jié)與展望

近年來(lái),隨著HPH技術(shù)發(fā)展和均質(zhì)機(jī)的革新與升級(jí),高壓均質(zhì)機(jī)的工作壓力和效率顯著提升,為流體食品殺菌提供了新選擇。HPH作為一種非熱加工技術(shù),不僅能夠保持食品原料的營(yíng)養(yǎng)品質(zhì)、提高產(chǎn)品穩(wěn)定性,而且還能夠有效殺滅微生物,保證食品安全,延長(zhǎng)貨架期。HPH技術(shù)在食品工業(yè)中具有潛在的應(yīng)用性,連續(xù)化生產(chǎn)的可操作性,能夠降低生產(chǎn)成本,提高生產(chǎn)效率。但是,現(xiàn)階段HPH還不能保證牛奶、豆奶、果汁、蛋制品等食品產(chǎn)品達(dá)到商業(yè)無(wú)菌的要求,同時(shí)存在均質(zhì)機(jī)耗能較大、在高壓工作條件下易損失較多、不適合于粘度較高的物料等技術(shù)局限性。HPH技術(shù)和裝備需要進(jìn)一步的發(fā)展?jié)M足工業(yè)化應(yīng)用的要求,包括:開發(fā)冷卻裝置降低均質(zhì)閥工作過(guò)程中引起料液溫度升高,開發(fā)新型材料提升均質(zhì)閥的耐腐蝕、抗壓、耐高溫性能,提高UHPH設(shè)備加工食品物料的工作效率,同時(shí)串聯(lián)清洗、無(wú)菌灌裝等設(shè)備,開發(fā)易于拆解和組裝的高壓均質(zhì)設(shè)備,便于日常維護(hù)和清洗。

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《食品工業(yè)科技》愿為企業(yè)鋪路、搭橋！

Reviewofhighpressurehomogenizationinliquidfoodsterilization

LIUWei1,SONGYi2,LIAOXiao-jun2,DONGPeng3,ZHANGJie1,LINQiong1,WUJie1,WANGZhi-dong1,*

(1. Institute of Agro-Products Processing Science and Technology CAAS,Ministry of Agriculture,Key Laboratory ofAgro-products Quality and Safety Control in Storage and Transport Process,Ministry of Agricultrue,Beijing 100193,China;2.National Engineering Research Center for Fruit and Vegetable Processing,Key Laboratory of Fruit and VegetableProcessing,Ministry of Agriculture,Research Center of Fruit and Vegetable Processing Engineering,Ministry ofEducation,College of Food Science and Nutritional Engineering,China Agricultural University,Beijing 100083,China;3. Technical Institute of Physics and Chemistry CAS,Beijing 100190,China)

High pressure homogenization(HPH)is a non-thermal processing technology. With the innovation and development of high pressure technology,modern homogenizers are able to withstand 400 MPa,which opens up new areas for food pasteurization and sterilization. The research showed that foodborne pathogen and spoilage microorganism could be damaged by shear,collision,hole,turbulence,worm,heating and other effects induced by HPH. In this paper,the working principle of HPH and related equipment are introduced. The research progress of this technology in food sterilization is discussed based on the factors such as microbiological,physical and chemical properties of foodstuffs and homogenization conditions,and the application prospect of this technology is analyzed.

high pressure homogenization;ultra high pressure homogenization;sterilization;microorganism;spore

2017-05-22

劉偉(1984-),男,博士,助理研究員,研究方向:果蔬貯藏和加工,E-mail:makebig@126.com。

*通訊作者:王志東(1958-),男,本科,研究員,研究方向:農(nóng)產(chǎn)品貯藏理論與技術(shù),E-mail:liuwei@caas.cn。

中國(guó)農(nóng)業(yè)科學(xué)院科技創(chuàng)新工程;國(guó)家重點(diǎn)研發(fā)計(jì)劃項(xiàng)目(2016YFD0400302)。

TS201.1

A

1002-0306(2017)23-0306-08

10.13386/j.issn1002-0306.2017.23.056