食品冷冻冷藏新发展

食品冷冻冷藏新发展李云飞2008年9月年人均消费水平年人均消费水平年人均消费水平0102030405060kg美国丹麦英国瑞典法国日本中国台湾上海冷冻产品状况冷冻产品状况冷冻产品状况肉类面食水产品果蔬冷饮果蔬12%水产品50%面食18%肉类20%冷饮28%易腐食品低温运输状况0102030405060708090100冷藏运输公路铁路发达国家中国(%)易腐食品低温贮藏状况53032170100100200300400500600低温库高温库全国上海万吨易腐食品低温贮藏状况（上海）0510152025303550607080902000年代库容量（万吨）植物组织结构特点动物组织结构特点冻结与解冻过程特点特点冻结解冻热导率W·(m·K)-12.20.5比热容kJ·(kg·K)-12.14.2食品与介质的温差可充分低不可充分高研究热点问题研究热点问题研究热点问题†速冻食品的质量问题快速冷冻技术超高压速冻技术部分玻璃化技术介电解冻技术†实现上述技术的装备†冷链建设与工艺管理问题降温速率与冰晶隧道式速冻机单体流化速冻机单体流化速冻机螺旋速冻机螺旋速冻机螺旋速冻机低温介质速冻机低温介质速冻机低温介质速冻机氢与电负性很强，且具有独立电子对、原子半径又较小的原子可形成氢键（如氮、氟）水的物理性质第VI族元素氢化物的融点和沸点H2O沸点融点H2SH2SeH2Te分子量温度/℃1000-60-1002040120800Thephasediagramofwater.lrepresentstheregioninwhichiceXIIhasbeenobservedbyLobbanetal.(T=260K,p=0.55GPa)[2].PleasenotethatthisregionisfullysurroundedbythestabilityrangeoficeV.TheinsetsketchesthepressureinducedtransitionlineofIh(redline)asstudiedbyO.Mishima[1].ThegreenareaindicatestheregioninwhichiceXIIissuccessfullyformed.HorizontalarrowsindicatethatIhtransformsbycompressionbelow150KtoiceXIIorhigh-densityamorphousstate(HDA)andabove150KtoiceIII/IX.Theorangeareadisplaysthe150KboundarystudiedbyO.MishimaforHDAwhichisequallyobservedforiceXII.冰晶类型TriplepointsMPa°CliquidgasIh0.0006120.01liquidIhIII209.9-21.985IhIIIII213-35IIIIIV344-24liquidIIIV350.1-16.986IIVVI626-70liquidVVI632.40.16VIVIIVIII21005liquidVIVII221681.6三相点参数密度变化冰晶形态－I型冰晶形态－III型冰晶形态－IV型TheH-bondframeworkofrhombohedraliceIVshowingtheauto-clathratearrangementwithH-bondspassingthroughthecentreof6memberedrings.冰晶形态－XII型TheH-bondframeworkoftetragonaliceXIITransitionoficeXIItowardshexagonaliceuponheating.Theupperleftphotographa)showsiceXIIasrecoveredfromthepressurecellatlowtemperature.Incontrasttohigh-densityamorphousiceithasamilkyappearance.ThefollowingphotographsshowtheflokingoficeXIIasittransformstothelowerdensityformscubiciceandhexagonalice(b-d).冰晶－XII型与冰晶－I型高压辅助冻结高压辅助冻结冰晶生长示意图冰晶生长形态高压辅助冻结质量高压辅助冻结质量高压切换冻结法高压切换冻结过程冰晶生长示意图Pressure-Shift-Freezing新鲜目鱼细胞Pressure-Shift-FreezingPressure-Shift-Freezing冻结与解冻过程解冻过程超高压容器柱塞结构高压系统高压冻结试验装置Pressure-Shift-FreezingPressure-shift-freezing(A)andpressureassistedthawing(B)ofpotatosatthephasediagramofwaterPressure-Shift-FreezingFreezingofpotatotissuewatertoiceIII几种冻结方式冰晶大小比较冷冻与玻璃化技术玻璃化形成过程玻璃化特性与温度关系玻璃态转变理论自由体积理论⎟⎠⎞⎜⎝⎛Δ=RTEBexpη链段能量与周围的自由体积大小冷冻稳定剂较高的T'g冷冻保护剂较强保水性影响玻璃化要素影响玻璃化要素玻璃态DSC曲线果蔬田间热与呼吸热TherespirationrateandtheproductionofCO2dependsmainlyonthestoragetemperature计算示例56.6103.09.02280=××kg水3101.155252056.61×=×kJ()3104.1725252.49.02280×=−×××kJ08.8204.09.02280=××kg水3108.206252008.82×=×kJ水的存在状态†自由水：在组织和细胞中容易结冰、也能溶解溶质的这部分水。毛细管水－－细胞间隙内水；滞化水－－组织内显微或亚显微结构与膜所阻留的水；流动水－－植物导管、细胞内液泡中的水。水的存在状态†束缚水：在组织内通过氢键与其它物质结合的这部分水。其特点是冰点低（约－40℃）；不能作为溶剂。溶质对冻结与蒸发温度的影响稀溶液中水的蒸气压比纯水蒸气压低sxppp⋅=−水溶液水在压力相同条件下，稀溶液中水的沸点高于纯水的沸点。sxKTT⋅−＝水溶液在压力相同条件下，稀溶液中水的冰点低于纯水的冰点。sxKTT⋅−＝溶液水叶面组织结构叶面表层气体运动叶面表层气体运动压力与蒸发温度压力与蒸发温度压力（Pa）温度（℃）压力（Pa）温度（℃）10130010087352339206110170615402-5123010260-10压力与蒸气体积1克水体积常温常压下1毫升873Pa，5℃下150000毫升RTMmPV=()278KKkmolJ8314180.001kgPa873=⋅====TRMmP压力与蒸气体积†如果每小时蒸发82kg水，则水蒸气体积达到0.15×82×1000＝12300m3。†需要真空泵抽出速率为205m3/min。抽出水蒸气保护油封泵冷阱的作用真空泵罗茨泵与油封泵性能10510310110-20255075100压强Pa抽气速率％影响真空预冷效果的因素™可用于汽化的水份含量；™表面组织的性质；™体表面积大小。果蔬材料果蔬堆放状态™果蔬堆放密度；™包装材料的气密性。设备性能™降压速率。风冷风冷负压风冷负压风冷水冷水冷水冷冰冷蒸发冷却Strawpackinghouse真空冷却真空冷却装货移动式真空冷却设备真空冷却冷却曲线Forced-AirHydroIceVacuumTypicalcoolingtime(hr)1-100.1-10.1-0.30.3-220-100Waterloss(%)0.1-20-0.5Nodata2-40.1-2Watercontactnoyesyes,unlessbaggednonoPotentialfordecaycontaminationlowhighlownonelowCapitalcostlowlowhighmediumlowEnergycostlowmediummediumhighlowWater-resistantpackagingneedednoyesyesnonoPortablesometimesrarelydonecommoncommonnoFeasibilityofin-linecoolingrarelydoneyesrarelydonecommonnoRoomComparisonofProduceEffectsandCostsforCommonCoolingMethods风冷运输风冷运输低温运输国外应用示例Productarrivesfromthefieldonlinetrucks.Someisthencooledbyicingandsomeisvacucooled.Vacuumcoolinginvolvesplacingcartonsofproduceinachamberwheretheatmosphericpressureislowered.国外应用示例Thiscausestheboilingpointofwatertodropanditisboiledoff.Coldwaterissimultaneouslyaddedtothecartonssotheproductemergescoldandundamaged.Regularicinginvolvespackingeachcartonofproducewithice.At25poundspercarton,weusetons!国外应用示例BonipakProduceCompanycanmanufacture300tonsoficeeachdayandwecanstore400tons.Whenlargequantitiesofproductcomeintothecooleroverashortperiod,wecooltheproduceinourAirTunnels.Wehave8tunnels,whichhold14palletsofproduceeach.Thecartonsarecoveredwithatarpandcoldairisthenforcedthroughtheholesinthecartons.国外应用示例Overaperiodofhours,theproduceisslowlycooledtothedesiredtemperature.Thermometersconstantlymonitortheprocesssotheproductisnotovercooled.Bye-Bye