李 俠,李 銀,張春暉※,鄧少穎,景曉亮,王春青(. 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)品加工綜合性重點(diǎn)實(shí)驗(yàn)室,北京 0093;. 雛鷹農(nóng)牧集團(tuán)股份有限公司,新鄭 4500)
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高氧氣調(diào)包裝對(duì)不同品種冷卻豬肉貯藏品質(zhì)及持水性的影響
李俠1,李銀1,張春暉1※,鄧少穎1,景曉亮2,王春青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)品加工綜合性重點(diǎn)實(shí)驗(yàn)室,北京 100193;2. 雛鷹農(nóng)牧集團(tuán)股份有限公司,新鄭 451100)
摘要:為了研究不同品種冷卻豬肉在高氧氣調(diào)包裝貯藏過(guò)程中,蛋白氧化對(duì)豬肉品質(zhì)及持水性的影響,試驗(yàn)以氟烷基因(NN)型杜長(zhǎng)大三元雜交豬和不含NN基因型的三門峽黑豬為研究對(duì)象,分析了2個(gè)品種豬肉經(jīng)高氧氣調(diào)包裝(80% O2+20% CO2),于(4±1)℃下貯藏過(guò)程中肌肉色澤、蛋白質(zhì)氧化、水分分布、保水性以及肌肉微觀結(jié)構(gòu)的變化。結(jié)果表明,隨著貯藏時(shí)間的延長(zhǎng)(0~10 d),2個(gè)品種豬肉的肌原纖維蛋白羰基含量顯著升高(P<0.05),巰基含量顯著降低(P<0.05),表明豬肉肌原纖維蛋白的氧化程度隨著貯藏時(shí)間的延長(zhǎng)而加??;肌原纖維蛋白發(fā)生持續(xù)性氧化,肌原纖維蛋白骨架的完整性遭到不同程度破壞,肌束膜破裂,纖維束間隙增大,結(jié)構(gòu)疏松,保水性降低,不易流動(dòng)水逐漸態(tài)變?yōu)樽杂伤?;與貯藏初始相比,第3天時(shí)杜長(zhǎng)大三元雜交豬和三門峽黑豬的不易流動(dòng)水均顯著降低(P<0.05),第5天杜長(zhǎng)大三元雜交豬的自由水顯著增加(P<0.05),而黑豬的自由水在第10天時(shí)顯著性增加(P<0.05);貯藏5 d以上時(shí),2個(gè)品種豬肉的蒸煮損失率均較對(duì)照組的蒸煮損失顯著增大(P<0.05);2個(gè)品種豬肉的L*值、ɑ*值、b*值均呈現(xiàn)先增加再降低的趨勢(shì),L*值在第7天時(shí)達(dá)到最大值,ɑ*值在第3天時(shí)達(dá)到最大值,杜長(zhǎng)大三元雜交豬和黑豬的b*值分別在第5天和第7天時(shí)達(dá)到最大值;2個(gè)品種的豬肉經(jīng)高氧氣調(diào)包裝,其色澤、蛋白質(zhì)氧化、水分態(tài)變、保水性、微觀結(jié)構(gòu)等指標(biāo)變化規(guī)律相似,表明高氧氣調(diào)包裝對(duì)2種豬肉的貯藏品質(zhì)及持水性的影響效應(yīng)具有一致性。研究結(jié)果為高氧氣調(diào)包裝冷卻豬肉貯藏品質(zhì)及汁液流失控制提供依據(jù)。
關(guān)鍵詞:貯藏;包裝;肉;冷卻豬肉;蛋白氧化;水分態(tài)變;微觀結(jié)構(gòu)
李俠,李銀,張春暉,鄧少穎,景曉亮,王春青. 高氧氣調(diào)包裝對(duì)不同品種冷卻豬肉貯藏品質(zhì)及持水性的影響[J]. 農(nóng)業(yè)工程學(xué)報(bào),2016,32(2):236-243.doi:10.11975/j.issn.1002-6819.2016.02.034http://www.tcsae.org
Li Xia, Li Yin, Zhang Chunhui, Deng Shaoying, Jing Xiaoliang, Wang Chunqing. Influence of high oxygen modified atmosphere packaging on different breeds of chilled pork meat quality and water holding capacity during storage[J]. Transactions of the Chinese Society of Agricultural Engineering (Transactions of the CSAE), 2016, 32(2): 236-243. (in Chinese with English abstract)doi:10.11975/j.issn.1002-6819.2016.02.034http://www.tcsae.org
冷卻肉是指將牲畜屠宰后,將其胴體在24 h內(nèi)降到0~4℃,并在后期的加工、流通及銷售過(guò)程中一直保持在此溫度范圍內(nèi)的生鮮肉。早在20世紀(jì)90年代,中國(guó)就已經(jīng)成為世界第一大肉類生產(chǎn)國(guó),而且冷卻肉的生產(chǎn)與銷售比例在逐年增加,但由于冷卻肉在貯藏、流通等過(guò)程中易受到污染,因而在保證冷卻肉品質(zhì)的同時(shí)延長(zhǎng)貯藏期對(duì)冷卻肉的發(fā)展具有非常重要的意義。目前對(duì)冷卻肉的保鮮技術(shù)研究主要集中在以下幾個(gè)方面:冰溫保鮮,將冷鮮肉的溫度保持在凍結(jié)點(diǎn)以上(約為?2℃)至0℃范圍內(nèi),可有限地維持冷卻肉的生理活性,同時(shí)保證不被凍結(jié),進(jìn)而達(dá)到保鮮的目的[1];超高壓保鮮技術(shù),對(duì)冷卻肉施加一定的壓力,可保持冷卻肉在色澤上的穩(wěn)定性[2];氣調(diào)包裝保鮮技術(shù),采用一種或多種混合氣體來(lái)抑制微生物的繁殖,減緩冷卻肉變質(zhì)[3]。高氧氣調(diào)包裝指以含有體積分?jǐn)?shù)為70%~80% O2和20%~30% CO2組合的方式對(duì)肉品進(jìn)行的包裝。對(duì)于紅肉而言,高體積分?jǐn)?shù)的O2可使鮮肉呈現(xiàn)穩(wěn)定的紅色,而CO2可以抑制細(xì)菌的生長(zhǎng)從而延長(zhǎng)貯藏期限。西方國(guó)家超市中銷售的冷卻肉多以高氧氣調(diào)包裝為主,可有效提高肉的安全性及抑制肉色褐變[4]。Ho等[5]研究發(fā)現(xiàn)用80% O2+20% CO2的高氧氣調(diào)包裝肉餡餅比用真空包裝和透氣性聚氯乙烯包裝能較好地延遲微生物的生長(zhǎng)。John 等[6]研究用80% O2包裝牛里脊肉排,發(fā)現(xiàn)在14天和21天貯藏期間牛肉保持了令人滿意的顏色。Martínez等[7]研究發(fā)現(xiàn)以80% O2+20% CO2的氣體組合來(lái)包裝新鮮豬肉香腸,能夠增強(qiáng)其紅色。
大多數(shù)研究多集中在如何包裝更適宜冷卻肉保鮮及護(hù)色,而對(duì)于冷卻肉在高氧氣調(diào)包裝環(huán)境下,肌肉蛋白氧化劣變、氧化介導(dǎo)的肌肉蛋白與水分的互作關(guān)系、水分狀態(tài)變化等方面鮮有研究。因此,本文選取氟烷基因型為NN的外引生豬品種(杜長(zhǎng)大三元雜交豬,杜洛克豬×長(zhǎng)白豬×大約克夏豬)與不含氟烷基因的中國(guó)地方品種(三門峽黑豬)的背最長(zhǎng)肌為研究對(duì)象,通過(guò)測(cè)定冷卻肉在高氧氣調(diào)包裝貯藏期間的色澤、蛋白氧化、水分狀態(tài)分布與變化、保水性以及超微結(jié)構(gòu)等指標(biāo),研究在貯藏過(guò)程中其品質(zhì)變化及水分態(tài)變機(jī)制,探討高氧氣調(diào)包裝條件下肌肉蛋白氧化、保水性與水分態(tài)變的互作關(guān)系,以期為高氧氣調(diào)包裝在肉類保質(zhì)、護(hù)色等方面提供理論依據(jù)。
1.1材料與儀器
試驗(yàn)材料由雛鷹集團(tuán)股份有限公司提供的月齡為6月、質(zhì)量為(100±5)kg的9頭杜長(zhǎng)大三元雜交豬(杜洛克豬×長(zhǎng)白豬×大約克夏豬)和9頭三門峽黑豬,采用電擊暈屠宰后,取左右兩側(cè)的背最長(zhǎng)肌后于4℃環(huán)境中成熟24 h,待用。
CR-400便捷式色差儀(柯尼卡美能達(dá)(日本)公司);電子天平(賽多利斯科學(xué)儀器(北京)有限公司);T6紫外可見(jiàn)分光光度計(jì)(北京普析通用儀器有限責(zé)任公司);Testo 735-2熱電偶(德國(guó)儀器國(guó)際貿(mào)易(上海)有限公司);7012G攪拌機(jī)(美國(guó)Waring公司);Eiko IB.5型離子濺射噴金儀(日本Hitachi公司);H-7500透射電鏡(日本Hitachi公司);Quanta 200 FEG 場(chǎng)發(fā)射環(huán)境掃描電子顯微鏡由國(guó)家納米中心提供;MesoMR型核磁共振分析與成像系統(tǒng)(上海紐邁電子科技有限公司)。
1.2試劑
5,5-二硫代雙(2-硝基苯甲酸)(5,5′-Dithio bis-(2-nitrobenzoic acid),DTNB)、乙二醇-雙-(2-氨基乙醚)四乙酸(Ethylene glycol bis (2-aminoethyl ether)-N, N, N′,N′-tetraacetic acid,EGTA)(美國(guó)sigma公司);牛血清白蛋白(bovine serum albumin,BSA)(北京拜爾迪生物技術(shù)有限公司);其他試劑均購(gòu)于國(guó)藥集團(tuán)化學(xué)試劑有限公司,均為分析純。
1.3試驗(yàn)方法
1.3.1試驗(yàn)設(shè)計(jì)
每條豬背最長(zhǎng)肌作為1個(gè)生物學(xué)重復(fù),分為2組,每組設(shè)置6個(gè)平行,試驗(yàn)重復(fù)3次。將成熟24 h后的豬背最長(zhǎng)肌修剪成長(zhǎng)度約為10 cm,厚度約為1.5 cm大小的豬肉塊,置于80% O2/20% CO2氣體組分的氣調(diào)包裝盒內(nèi)冷藏(0~4℃)保鮮,包裝盒內(nèi)的氣體與樣品體積比為3:1,包裝材料為透氧率0.21 cm3/(m2·d)的高阻隔材料。測(cè)定空白肉樣的含水率、蛋白質(zhì)含量、肌內(nèi)脂肪含量、肌紅蛋白含量、氧合肌紅蛋白含量、高鐵肌紅蛋白含量,并在貯藏期間分別測(cè)定0、1、3、5、7、10 d肉樣的蛋白氧化及品質(zhì)指標(biāo),以宰后0~4℃成熟24 h的新鮮豬背最長(zhǎng)肌為空白對(duì)照。
1.3.2品質(zhì)指標(biāo)的測(cè)定
含水率的測(cè)定參照GB/T 9695.15-2008;蛋白質(zhì)含量的測(cè)定參照GB/T 5009.5-2003;肌內(nèi)脂肪含量的測(cè)定參照GB/T 9695.7-2008;肌紅蛋白含量的測(cè)定參照謝小雷等[8]方法。
氟烷基因(NN)型杜長(zhǎng)大三元雜交豬和不含NN的三門峽黑豬是目前國(guó)內(nèi)豬肉生產(chǎn)的典型代表品種,杜長(zhǎng)大三元雜交豬生長(zhǎng)速度快、抗病力強(qiáng)、胴體瘦肉率高;三門峽黑豬是中國(guó)“生態(tài)原產(chǎn)地保護(hù)”地方豬種,具有繁殖力高、肉質(zhì)優(yōu)良、肉色好等優(yōu)點(diǎn)。杜長(zhǎng)大三元雜交豬和三門峽黑豬基本品質(zhì)指標(biāo)見(jiàn)表1。
色差的測(cè)定:用便捷式色差儀直接測(cè)定樣品表面的肉色,結(jié)果以L*(亮度)、ɑ*(紅度)、b*(黃度)的形式記錄。
表1 杜長(zhǎng)大三元雜交豬和三門峽黑豬基本品質(zhì)指標(biāo)Table 1 Basic quality index of crossbred pig and Sanmenxia black pig
肌原纖維蛋白的提取:參考潘君慧[9]的方法提取,并用提取液將蛋白濃度稀釋為2 mg/mL,稀釋后的蛋白溶液用以羰基含量和巰基含量的測(cè)定。
羰基含量的測(cè)定:參考Levine等[10]方法并略作修改。取0.1 mL稀釋后的蛋白溶液,然后加入0.5 mL 2 mol/L HCl溶液(含10 mmol/L 2,4-二硝基苯肼),空白樣品中加入0.5 mL 2 mol/L HCl溶液。溶液混勻于室溫下靜置40 min后,再加入0.5 mL 20%的三氯乙酸混勻,于11 000×g,4℃條件下離心5 min,棄去上清液,沉淀用乙醇-乙酸乙酯溶液(體積比為1:1)洗滌3次后,再將沉淀懸浮于1 mL 6 mol/L鹽酸胍溶液中,在37℃水浴中保溫30 min后,于370 nm波長(zhǎng)下測(cè)定吸光值,蛋白羰基含量(nmol/mg)使用摩爾吸光系數(shù)22 000 L/(mol·cm)計(jì)算。
巰基含量的測(cè)定:參考李銀等[11]方法并稍作修改。取1 mL稀釋后的蛋白溶液,加入1 mL 50 mmol/L Tris-HCl 緩沖液(pH值8.3)(含6 mol/L鹽酸胍、1 mmol/L EDTA)及10 μL 100 mmol/L Tris-HCl 溶液(pH值7.6)(含10 mmol/L DTNB),將上述溶液混勻后室溫下靜置25 min,于412 nm波長(zhǎng)下測(cè)定吸光值,巰基含量(nmol/mg)使用摩爾吸光系數(shù)13 600 L/(mol·cm)計(jì)算。
1.3.3持水性的測(cè)定
肌肉中水分分布與組成的測(cè)定:參考Li等[12]的方法,采用低場(chǎng)核磁共振(low-field nuclear magnetic resonance,LF-NMR)測(cè)定豬肉中水分的橫向弛豫時(shí)間T2。測(cè)定條件:主頻率為23.29 MHz,90°脈沖與180°脈沖之間的τ-值為200 μs,累積6次,重復(fù)間隔時(shí)間3 000 ms,回波個(gè)數(shù)為2 000,所得Carr-Purcell-Meiboom-Gill(CPMG)指數(shù)衰減曲線采用儀器自帶的MultiExp Inv Analysis 軟件進(jìn)行反演得到T2值。T21、T22及T23分別對(duì)應(yīng)結(jié)合水、不易流動(dòng)水及自由水,并通過(guò)峰面積計(jì)算得到3種水分的百分比。
氫質(zhì)子密度成像測(cè)定:參考謝小雷等[13]和徐建國(guó)等[14]的方法并稍加修改。將待測(cè)樣品切成5 cm×3 cm×3 cm長(zhǎng)方體小條,放入永磁場(chǎng)中心位置的射頻線圈中心,通過(guò)MSE成像序列得到肌肉的氫質(zhì)子密度成像圖,主要參數(shù)為:重復(fù)時(shí)間500 ms,回波時(shí)間20 ms,中心頻率23.29 MHz,縱向視野寬度和橫向視野寬度均為50 mm。
肌肉蒸煮損失的測(cè)定:參考Li等[15]的方法,準(zhǔn)確稱量肉塊的質(zhì)量后將其置于蒸煮袋中,于80℃水浴中加熱至肉中心溫度75℃后,立即取出于冰水中冷卻至中心溫度25℃,用吸水紙吸干肉樣表面水分并精確稱量肉塊質(zhì)量。蒸煮損失率計(jì)算公式如下
1.3.4肌肉微觀結(jié)構(gòu)觀察
通過(guò)掃描電鏡和透射電鏡觀察貯藏過(guò)程中豬肉背最長(zhǎng)肌微觀結(jié)構(gòu)的變化。
掃描電鏡(scanning electron microscrope,SEM)觀察參照Palka和Daun的方法[16]。將待檢測(cè)肉樣沿肌纖維的方向切成5 mm×5 mm×2 mm的肉塊,于質(zhì)量分?jǐn)?shù)為2.5%戊二醛溶液中固定24 h后用0.1 mol/L的磷酸鹽緩沖液(pH值7.3)沖洗3次,室溫靜置2 h后,用蒸餾水將固定好的肉樣沖洗干凈,再依次用體積分?jǐn)?shù)為25%、50%、70%、95%及100%的乙醇溶液各脫水2次(每次1 h)。隨后將其在超臨界CO2干燥儀中凍干,并經(jīng)置換、噴金后,用掃描電鏡于500×下觀察、拍照。
透射電鏡(transimission electron microscrope,TEM)觀察參考Li等[17]的方法。將待測(cè)肉樣沿肌纖維的方向切成4 mm×4 mm×2 mm的肉塊,于質(zhì)量分?jǐn)?shù)為2.5%的戊二醛溶液中固定24 h后,用0.1 mol/L的磷酸緩沖液(pH 值7.3)沖洗3次,然后用質(zhì)量分?jǐn)?shù)為2%四氧化鋨二次固定后,再依次用體積分?jǐn)?shù)為30%、50%、70%、80%、90%、95%及100%的乙醇溶液脫水2次(每次1 h),脫水后的肉樣用618#環(huán)氧樹脂進(jìn)行包埋,再用超薄切片機(jī)進(jìn)行超薄切片,切片用醋酸鈾-檸檬酸鉛雙染色,用透射電鏡于25 000×下觀察、拍照。
1.4數(shù)據(jù)分析
數(shù)據(jù)采用SAS9.2軟件進(jìn)行方差分析,不同處理間差異采用Duncan多重比較,顯著水平為P<0.05。
2.1貯藏過(guò)程中肌肉色澤變化
肉色是影響消費(fèi)者喜好的重要因素之一,亦是肉類感官品質(zhì)的重要指標(biāo)[18]。肉的顏色可通過(guò)亮度值(L*),紅度值(ɑ*)和黃度值(b*)來(lái)衡量,其中L*與肉樣表面含水率密切相關(guān),反映肉的表面白度;ɑ*對(duì)于豬肉、羊肉、牛肉等“紅肉”而言,ɑ*值越高,說(shuō)明肉樣色澤越好,肉越新鮮;b*在一定范圍內(nèi)對(duì)肉色的影響與ɑ*值類似,但影響效果較小[19]。
由表2可知,隨著貯藏時(shí)間的延長(zhǎng),杜長(zhǎng)大三元雜交豬和三門峽黑豬的L*值均呈顯著增加的趨勢(shì)(P<0.05),在貯藏后期(7~10 d),L*值達(dá)最大值,表明肉樣因汁液滲出導(dǎo)致表面含水率增高,對(duì)光的反射作用增強(qiáng)[19];在不同貯藏階段,杜長(zhǎng)大三元雜交豬的L*值均高于黑豬,這表明在貯藏過(guò)程中,前者的自由水相對(duì)百分比高于后者(表3),這可能與杜長(zhǎng)大三元雜交豬的肌肉含水率較高(表1)及保水性有關(guān)。2個(gè)品種肉樣的ɑ*值均呈先升高后顯著降低的趨勢(shì),在第3天時(shí)達(dá)到最大值后,呈顯著降低趨勢(shì);在貯藏初期,由于氧氣濃度較高,與肌紅蛋白結(jié)合,生成亮紅色的氧合肌紅蛋白(鮮紅色),ɑ*值升高;但隨著貯藏時(shí)間的延長(zhǎng),氧合肌紅蛋白被進(jìn)一步氧化成高鐵肌紅蛋白(呈褐色),ɑ*值降低[20];因三門峽黑豬肌肉中氧合肌紅蛋白含量高于杜長(zhǎng)大三元雜交豬(表1),而呈現(xiàn)較好的色澤。b*值的變化趨勢(shì)與ɑ*值相似,三門峽黑豬在第7天達(dá)到最大,杜長(zhǎng)大三元雜交豬在第5天達(dá)到最大,也與貯藏過(guò)程中肌紅蛋白發(fā)生氧化反應(yīng)生成高鐵肌紅蛋白相關(guān)[21]。
表2 豬肉貯藏過(guò)程中色澤變化Table 2 Change of CIE* color of pig during storage
2.2貯藏過(guò)程中肌肉蛋白羰基和巰基含量變化
蛋白肽鏈上帶有NH及NH2基團(tuán)的氨基酸側(cè)鏈?zhǔn)艿阶杂苫墓魯嗔研纬婶驶?,羰基值越大蛋白氧化程度越大[12]。因此分析2個(gè)品種豬肉在貯藏過(guò)程中羰基含量變化,可以反映冷卻肉在高氧氣調(diào)包裝條件下蛋白氧化程度及其品質(zhì)變化。由圖1a可以看出,隨著貯藏時(shí)間的延長(zhǎng),三門峽黑豬和杜長(zhǎng)大三元雜交豬的羰基含量均呈顯著性增加的趨勢(shì)(P<0.05),肌原纖維蛋白的氨基酸側(cè)鏈或是肽鏈在貯藏體系中被攻擊使其斷裂而導(dǎo)致羰基含量的增加[22],表明在高氧氣調(diào)包裝條件下,2個(gè)品種的豬肉都發(fā)生了顯著的蛋白氧化現(xiàn)象;在相同的貯藏時(shí)間點(diǎn)(除第7天外),黑豬的羰基含量略低于杜長(zhǎng)大三元雜交豬,2種豬肉經(jīng)高氧氣調(diào)包裝貯藏,其蛋白氧化情況相似。
巰基對(duì)于穩(wěn)定肌原纖維蛋白完整的空間結(jié)構(gòu)具有非常重要的意義。肌球蛋白和肌動(dòng)蛋白是肌原纖維蛋白中含量最高的2種蛋白質(zhì),肌球蛋白分子中約含有42個(gè)巰基,肌動(dòng)蛋白分子中約含有12個(gè)巰基。巰基(-SH)氧化形成二硫鍵(-S-S-)[23],因此,分析巰基含量的變化可以從另一個(gè)方面反映在高氧氣調(diào)包裝條件下的蛋白質(zhì)氧化效應(yīng)。由圖1b可知,在貯藏過(guò)程中杜長(zhǎng)大三元雜交豬和三門峽黑豬的巰基含量均隨著貯藏時(shí)間的延長(zhǎng)而逐漸減少,杜長(zhǎng)大三元雜交豬的巰基含量在第3天時(shí)顯著(P<0.05)低于貯藏初始時(shí)和第1天,三門峽黑豬的巰基含量在初始時(shí)為117.14 nmol/mg顯著(P<0.05)高于其他貯藏天數(shù)。巰基含量的顯著降低可能是由于蛋白質(zhì)空間結(jié)構(gòu)伸展,使得臨近的-SH相互作用形成二硫鍵[11],從而直觀地反映出蛋白質(zhì)的氧化程度。
圖1 豬肉貯藏過(guò)程中蛋白羰基和巰基含量變化Fig.1 Change of protein carbonyl and sulfydryl content of pig during storage time
2.3貯藏過(guò)程中肌肉中水分分布與組成變化
通過(guò)低場(chǎng)核磁共振技術(shù)檢測(cè)肉品中氫原子核在磁場(chǎng)中的弛豫性[24-25],利用T2值可以分析豬肉在高氧氣調(diào)包裝貯藏下,肉中3種狀態(tài)水(結(jié)合水、不易流動(dòng)水及自由水)的分布及組成變化情況[26]。
本研究借助LF-NMR對(duì)肌肉中結(jié)合水(0.1~10 ms)、不易流動(dòng)水(10~100 ms)和自由水(100~1 000 ms)的含量進(jìn)行檢測(cè)[25],并將3種狀態(tài)水的百分比分別記為P21、P22及P23(表3)。由表3可知,在高氧氣調(diào)包裝貯藏期間,2個(gè)品種豬肉在貯藏期間的3種狀態(tài)水發(fā)生了顯著變化(P<0.05)。隨著貯藏時(shí)間的延長(zhǎng),2種品種豬肉中結(jié)合水(P21)百分比總體呈上升趨勢(shì),但含量變化不大,三門峽黑豬中的結(jié)合水百分比從7.43%上升到9.04%,杜長(zhǎng)大三元雜交豬肉中結(jié)合水百分比從7.86%上升到9.40%;在貯藏過(guò)程中,2個(gè)品種豬肉的不易流動(dòng)水(P22)百分比呈持續(xù)降低的趨勢(shì),三門峽黑豬和杜長(zhǎng)大三元雜交豬中的不易流動(dòng)水百分比由初始的91.86%和91.26%分別降低到第10天的86.74%和86.08%;而2種品種豬肉中的自由水(P23)百分比均呈持續(xù)增加的趨勢(shì),三門峽黑豬和杜長(zhǎng)大三元雜交豬分別從初始的0.71%和0.88%上升到第10天的4.22%和4.53%,分別增加了5.9倍、5.1倍。根據(jù)P21、P22與P23百分比的消長(zhǎng)趨勢(shì),表明在貯藏期間肌肉中不同狀態(tài)水之間發(fā)生了相互轉(zhuǎn)化。在貯藏期間,由于肌纖維結(jié)構(gòu)收縮將位于肌纖維細(xì)胞內(nèi)的水分“擠出”而流向細(xì)胞外,不易流動(dòng)水P22下降,自由水P23增加,肌肉持水性下降,造成汁液流失[26];肌原纖維蛋白氧化、降解,改變了蛋白結(jié)構(gòu),蛋白表面疏水殘基與親水殘基發(fā)生變化,導(dǎo)致蛋白表面疏水性上升,肌肉中不易流動(dòng)水P22下降,自由水P23增加,不易流動(dòng)水態(tài)變?yōu)樽杂伤?,成為新的汁液流失?lái)源。Bertram等[25]對(duì)豬肉的P22與滴水損失相關(guān)性研究結(jié)果也得出了相似的結(jié)論。
表3 豬肉在貯藏過(guò)程中水分分布及組成變化Table 3 Change of water distribution and composition of pig during storage
2.4貯藏過(guò)程中肌肉水分空間分布的變化
核磁共振成像技術(shù)可在不損壞肉樣的條件下,將肉樣內(nèi)部的H質(zhì)子產(chǎn)生的信號(hào)轉(zhuǎn)變成密度圖譜,反映肉樣中水分的空間分布情況,圖譜褐色面積越大,亮度值越大,表明H質(zhì)子密度越高,信號(hào)越強(qiáng),該區(qū)域的含水率越高。圖2為三門峽黑豬和杜長(zhǎng)大三元雜交豬在高氧氣調(diào)包裝條件下,不同貯藏時(shí)間的二維H質(zhì)子密度圖譜。由圖可以看出,隨著貯藏時(shí)間的延長(zhǎng),2種品種豬肉的H質(zhì)子密度圖像的褐色面積均呈逐漸降低的趨勢(shì),表明肉中的總含水率逐漸減少。三門峽黑豬的H質(zhì)子密度圖譜在第3天時(shí),褐色面積明顯減少,而杜長(zhǎng)大三元雜交豬的密度圖譜在第5天時(shí),褐色面積明顯減少,含水率明顯降低。Li等[15]研究表明,肌原纖維蛋白的氧化程度和肌肉貯藏汁液流失密切相關(guān),由羰基、巰基含量變化可知(圖1),隨著貯藏時(shí)間的延長(zhǎng),三門峽黑豬和杜長(zhǎng)大三元雜交豬的肌原纖維蛋白氧化加劇,肌原纖維蛋白骨架嚴(yán)重破壞,肌肉的持水性降低,汁液流失加劇,從而影響肉中水分的含量和分布。
圖2 豬肉在貯藏過(guò)程中H質(zhì)子密度圖像變化Fig.2 Change of proton density image of pig during storage
2.5貯藏過(guò)程中肌肉保水性變化
肌肉保水性是肉品一項(xiàng)非常重要的經(jīng)濟(jì)指標(biāo),同時(shí)亦對(duì)肉的食用品質(zhì)有著重要的影響。冷鮮肉在貯藏過(guò)程中發(fā)生汁液流失,造成經(jīng)濟(jì)損失、嫩度降低、營(yíng)養(yǎng)價(jià)值損失等。通過(guò)測(cè)定豬肉的蒸煮損失率可以表征豬肉的保水性。由表4知,隨著貯藏時(shí)間的延長(zhǎng),2個(gè)品種豬肉的蒸煮損失率均顯著增加(P<0.05),黑豬的蒸煮損失率略低于白豬,可能與2個(gè)品種豬肉的含水率(表1)及持水性不同有關(guān)[27],高氧氣調(diào)包裝對(duì)2種不同豬肉貯藏過(guò)程中蒸煮損失率的影響效應(yīng)相似。
表4 豬肉貯藏過(guò)程中蒸煮損失率變化Table 4 Change of cooking loss of pig during storage
2.6貯藏過(guò)程中肌肉微觀結(jié)構(gòu)變化
通過(guò)電鏡觀察肌肉的微觀結(jié)構(gòu),研究在高氧氣調(diào)包裝貯藏過(guò)程中肌肉微觀結(jié)構(gòu)的變化。圖3為三門峽黑豬和杜長(zhǎng)大三元雜交豬在高氧氣調(diào)包裝條件下不同貯藏時(shí)間微觀結(jié)構(gòu)的掃描電鏡圖及透射電鏡圖。
圖3 豬肉在貯藏過(guò)程中微觀結(jié)構(gòu)的變化Fig.3 Change of microstructure of pig during storage
由圖3a知,在貯藏過(guò)程中,三門峽黑豬和杜長(zhǎng)大三元雜交豬的肌原纖維骨架蛋白降解,肌肉的微觀結(jié)構(gòu)遭到不同程度的破壞。隨著貯藏時(shí)間的延長(zhǎng),蛋白骨架結(jié)構(gòu)的破壞程度加大,主要表現(xiàn)為肌原纖維束疏松,肌束間隙變大,肌束膜破壞,導(dǎo)致肌原纖維蛋白的持水性降低,汁液流失嚴(yán)重。陳韜等[28]研究表明肌原纖維的完整性與肌肉的保水特性具有顯著的相關(guān)性。由圖3b知,初始時(shí)三門峽黑豬和杜長(zhǎng)大三元雜交豬的肌原纖維結(jié)構(gòu)完整,肌絲排列整齊,A帶和I帶清晰可辨,Z線和M線明顯;第1天時(shí),三門峽黑豬的I帶和A帶仍清晰可見(jiàn),Z線、M線保持完整,而杜長(zhǎng)大三元雜交豬的M線清晰可辨,Z線開始模糊;當(dāng)貯藏第5天時(shí),三門峽黑豬的超微結(jié)構(gòu)降解嚴(yán)重,I帶破壞嚴(yán)重,Z線周圍細(xì)絲部分?jǐn)嗔眩琈線模糊;而杜長(zhǎng)大三元雜交豬的肌原纖維結(jié)構(gòu)在貯藏期達(dá)到第3天時(shí),Z線就開始發(fā)生部分降解,其周圍的細(xì)絲開始發(fā)生斷裂;當(dāng)?shù)?天時(shí),杜長(zhǎng)大三元雜交豬和三門峽黑豬的肌原纖維結(jié)構(gòu)模糊,Z線和M線斷裂消失。隨著貯藏時(shí)間的延長(zhǎng),肌節(jié)逐漸發(fā)生崩解,I帶和A帶均被破壞,同時(shí)發(fā)生肌節(jié)收縮現(xiàn)象,杜長(zhǎng)大三元雜交豬的收縮率要高于三門峽黑豬,肌纖維結(jié)構(gòu)的收縮將細(xì)胞內(nèi)的水分“擠出”,自由水含量增加,肌肉的保水性下降,蒸煮損失率增大。這與Wattanachant等[29]研究雞肉組織超微結(jié)構(gòu)與肌肉保水性的的結(jié)論相似。
本試驗(yàn)研究了在高氧氣調(diào)包裝條件下,杜長(zhǎng)大三元雜交豬和三門峽黑豬在貯藏過(guò)程中肌肉品質(zhì)和持水性的變化。研究表明,隨著貯藏時(shí)間的延長(zhǎng),杜長(zhǎng)大三元雜交豬和三門峽黑豬的羰基含量由初始時(shí)的0.67 nmol/mg 和0.59 nmol/mg升高到第10天的3.39和3.27 nmol/mg,巰基含量由初始時(shí)的108.64和117.14 nmol/mg降低到第10天的50.959和53.481 nmol/mg,2個(gè)品種豬肉肌原纖維蛋白氧化程度逐漸加深;肌肉色澤(L*、ɑ*、b*值)隨著貯藏時(shí)間的延長(zhǎng)先增加后降低;肌原纖維蛋白的完整骨架結(jié)構(gòu)遭到的破壞,肌束膜破裂,纖維束間隙增大,結(jié)構(gòu)疏松,保水性降低;肌肉中一部分不易流動(dòng)水“態(tài)變”為自由水,導(dǎo)致蒸煮損失增大。高氧氣調(diào)包裝對(duì)2個(gè)品種豬肉在不同貯藏階段的色澤、蛋白質(zhì)氧化、水分含量和分布、超微結(jié)構(gòu)等影響效應(yīng)具有相似性。
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Influence of high oxygen modified atmosphere packaging on different breeds of chilled pork meat quality and water holding capacity during storage
Li Xia1, Li Yin1, Zhang Chunhui1※, Deng Shaoying1, Jing Xiaoliang2, Wang Chunqing1
(1. Institute of Agro-Products Processing Science ɑnd Technology, Chinese Acɑdemy of Agriculturɑl Sciences/Comprehensive Key
Lɑborɑtory of Agro-Products Processing, Ministry of Agriculture, Beijing 100193, Chinɑ; 2. ChuYing Agro-pɑstorɑl Group Co.Ltd, Xinzheng 451100, Chinɑ)
Abstract:Pork is one of the most commonly consumed meat worldwide, and its quality has received great attention. Pork quality is evaluated by edible quality, nutritional quality, health and safety quality and technical quality, and consumers often rate meat by their nutritional quality and edible quality, which are mainly determined by protein content, meat tenderness and water retention. Meat tenderness has a good linear correlation with cooking loss. Since the chilled meat is susceptible to contamination during the process of storage and circulation, ensuring the quality of chilled meat and meanwhile extending the storage period have great significance for the development of chilled meat. High oxygen modified atmosphere is a new packaging technique, which usually contains 70%-80% oxygen and 20%-30% carbon dioxide and can effectively extend the shelf life of meat. Oxygen can ensure the stabilization of meats’ red color and carbon dioxide will prolong the shelf life of meats by inhibiting the microorganism growth. Meat in the high oxygen modified atmosphere packaging will produce a series of complex physical and chemical and biochemical changes, and these changes have important influence on the quality. The investigate the protein oxidation effect on pork quality and water holding capacity when the different varieties chilled pork were stored in high oxygen modified atmosphere packaging. Crossbred pigs (Duroc × Landrace × Yorkshire) (with halothane genotype NN) and Sanmenxia black pigs (without halothane NN gene) were used in this experiment. The changes of CIE* color (L*, ɑ*, b*), protein oxidation, water distribution, water holding capacity and muscle microstructure during the storage at 4℃ in high oxygen modified atmosphere packaging (80% O2+ 20% CO2) were determined. The results showed that with the extension of storage time (0-10 day), carbonyl content increased significantly (P<0.05) and sulfhydryl content declined significantly (P<0.05). The results also showed that myofibril protein oxidation from the 2 types of pigs became more severe with the extension of storage time, which induced the breakdown of the structure of myofibrils. The microstructure of the myofibrils was altered obviously, which was indicated by perimysium rupture, increasing of space between fibers, and loose structure. It was observed that immobilized water converted to free water and thus water holding capacity decreased. Immobilized water of both the crossbred pigs and the black pigs declined significantly (P<0.05) at the 3rdday compared with the control. Compared with that of the control (at the initial state), free water in the meat of the crossbred pigs and the black pigs on the 3rdday decreased, while it increased significantly (P<0.05) on the 5thdayfor the crossbred pigs and on the 10thday for the black pigs, respectively. Cooking losses of the meat from 2 breeds of pigs increased significantly compared with that of control (P<0.05) when the storage time was longer than 5 d. Meanwhile, CIE* colors of the 2 breeds of pigs were increased at first and then decreased. The L* values of meat from the 2 breeds of pigs reached the maximum on the 7thday. The ɑ* values reached the maximum on the 3rdday. The b* values of meat from the crossbred pigs and black pigs reached the maximum value on the 5thand 7thday, respectively. Results show that high oxygen modified atmosphere packaging has the similar effects on CIE* color, protein oxidation, water state change, water holding capacity and microstructure of meat from the 2 breeds of pigs, which indicates that the effects of high oxygen modified atmosphere packaging on pork meat quality and water holding capacity are universal. The results provide the basis for control pork quality and cooking loss during cooling meat storaged in high oxygen modified atmosphere packaging.
Keywords:storage; packaging; meats; chilled pig; protein oxidation; myowater state changes; microstructure
通信作者:※張春暉,男,河南固始人,研究員,博士生導(dǎo)師,研究方向?yàn)槿馄房茖W(xué)。北京中國(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)品加工綜合性重點(diǎn)實(shí)驗(yàn)室,100193。Email:dr_zch@163.com
作者簡(jiǎn)介:李 俠,女,內(nèi)蒙古呼倫貝爾人,助理研究員,研究方向?yàn)槿馄房茖W(xué)。北京中國(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)品加工綜合性重點(diǎn)實(shí)驗(yàn)室,100193。Email:lixia5299@163.com
基金項(xiàng)目:國(guó)家自然科學(xué)基金項(xiàng)目(31371797,31571787);公益性行業(yè)(農(nóng)業(yè))科研專項(xiàng)(201303083)
收稿日期:2015-09-22
修訂日期:2015-10-26
中圖分類號(hào):TS251.1
文獻(xiàn)標(biāo)志碼:A
文章編號(hào):1002-6819(2016)-02-0236-08
doi:10.11975/j.issn.1002-6819.2016.02.034