食品化學(xué)重點(diǎn)

1、第二章 水2. 水的結(jié)構(gòu)F 混合式 ：分子間氫鍵瞬時地濃集在水分子中F 連續(xù)式：分子間氫鍵均勻分布在整個試樣中F 填隙式：水以一種籠形物結(jié)構(gòu)存在F 占優(yōu)勢的結(jié)構(gòu)：在短暫和扭曲的四面體中液態(tài)水通過氫鍵而締合F 氫鍵鍵合排列的高度動態(tài)性導(dǎo)致了黏度低。持水力（Water holding capacity）：F 由分子（以低濃度存在的大分子）構(gòu)成的基體通過物理方式截留大量水而阻止水滲出的能力。5. 水的分類F 食品中水的存在形式F 食品中的水: 結(jié)合水和體相水F 結(jié)合水：構(gòu)成水 鄰近水 多層水 F 體相水：截留水 自由水結(jié)合水(bound water)定義 ：存在于溶質(zhì)及其它非水組分鄰近的水。 構(gòu)成水

2、(constitutional water) 結(jié)合最強(qiáng)的水，已成為非水物質(zhì)的整體部分 鄰近水(vicinal water) 占據(jù)著非水成分的大多數(shù)親水基團(tuán)的第一層位置 多層水(multilayer water) 占有第一層中剩下位置及形成了鄰近水外的幾層 7.水分活度：Aw=f/f0, f is the fugacity of the solvent and f0 is the fugacity of the pure solvent.At low pressures, the difference between f/f0 and p/p0 is less than 1%, so defin

3、ing Awp/p0, pure water: p=p0, Aw=1; in food, p is less than p0, so Aw<1. 在低壓下，與相對蒸汽壓之間的差別非常小，小于1%，因此AwP/Po，純水：P=P0，Aw=1；食品中P總小于P0，故Aw<1F 水分活度的意義：First, at above-freezing T, Aw is a function of sample composition and temperature, with the former factor predominating. At subfreezing T, Aw become

4、s independent of sample composition and depends solely on T. F 首先，冰點(diǎn)以上水分活度是樣品組成與溫度的函數(shù)，且樣品組成起著重要的作用；冰點(diǎn)以下水分活度與樣品組成無關(guān)，僅與溫度有關(guān)Second, Aw above-freezing temperature indicate the available water content of the sample, and describe the food stability, whereas, Aw subfreezing temperature cannot. F 第二，冰點(diǎn)以上水分活

5、度可反映體系中可利用的水的含量，可描述食品體系的穩(wěn)定性；冰點(diǎn)以下水分活度僅與冰的穩(wěn)定狀態(tài)有關(guān)，不能用以描述食品體系穩(wěn)定性。8.Moisture Sorption Isotherms (MSI)水分吸附特性曲線F Definition: A plot of water content of food versus Aw at constant temperature三個區(qū)間水的性質(zhì)F The properties of water from Zone:constitutional water; 這部分水屬于構(gòu)成水 00.07g H2O/ g dry matter; Aw: 00.25；在-40不

6、結(jié)冰；不能作為溶劑，含量很小，不足以產(chǎn)生對固體的增塑效應(yīng)unfreezable at -40, no ability to dissolve solutes, and no effect on the solid. stability, various rate of reaction is very low. 這部分水很難發(fā)生物理、化學(xué)變化，含此水分的食品的劣變速度也很慢。 F The properties of water from ZoneRange: 0.070.38g H2O/g dry matter, Aw=0.250.85 Less mobile than bulk water;

7、 流動性比整體相水稍差 Most of it is unfreezable at -40; 大部分水在-40不凍結(jié) Cause incipient swelling of the solid matrix.Water in Zones and constitutes less than 5% 區(qū)和區(qū)的水最多占5%F The properties of water from Zone>0.40g/g dry matter; Aw=0.850.99Bulk water is physically entrapped; 體相水被物理截留 Dissolution and dilution act

8、ion; 這部分水起到溶解和稀釋作用 可結(jié)冰；可作為溶劑 化學(xué)反應(yīng)也易于進(jìn)行；促進(jìn)微生物生長 Freezable and solvent;Chemical reaction and microorganisms is rapid; 區(qū)的體相水占高水分食品總水分的95%以上 Constitute more than 95% of the total water.9. 滯后現(xiàn)象 Hysteresis: Isotherm prepared by resorption does not be superimposable on isotherm prepared by desorption. 水分回吸

9、和解吸等溫線之間的不一致就稱為滯后現(xiàn)象 10. 脂肪氧化速度與水分活度的關(guān)系F At Aw=0.750.84, lipid oxidation in strained meat from chicken and pork proceeds much more rapidly by desorption. 將雞肉和豬肉的水分活度調(diào)至0.750.84，用解吸方法時脂肪氧化速度要高于用回吸的方法F Aw：0BET , the rate of lipid oxidation decreases; overdrying of samples; less than optimum stability. A

10、w在0BET范圍內(nèi)，氧化速度逐漸下降，試樣會過分干燥會導(dǎo)致食品穩(wěn)定性下降 F (原因是水與氧化產(chǎn)物結(jié)合，阻礙分解，阻止了氧化進(jìn)程) F AwBET, increasing rates of oxidation. AwBET時，氧化速度增加，因?yàn)樗痔岣吡搜醯娜芙舛?，促使大分子腫脹，從而暴露更多的催化部位，加速了氧化進(jìn)程。 F Aw0.80, retard rates of oxidation, and the dilution of catalysts reduces their effectivenessAw0.80，加入的水能阻滯氧化，催化劑也被水稀釋，從而降低了氧化效率。(一，水是一個產(chǎn)

11、物，水含量的繼續(xù)增加會導(dǎo)致產(chǎn)物的抑制作用； 二，當(dāng)試樣中水分含量已達(dá)到一定的水平時，促進(jìn)反應(yīng)速度的成分的溶解度，可接近性和流動性不再是速度限制因素，進(jìn)一步加水將稀釋速度限制成分，從而降低反應(yīng)速度 )第三章 碳水化合物 1 糖的分類：單糖、低聚糖、多糖Monosaccharide單糖: not be broken down to lower molecular weight carbohydrates by hydrolysis.Oligosaccharide低聚糖: contain 2 to 10 sugar units joined by glycosidic bonds.Polysacch

12、aride多糖: are polymers of monosaccharides. 2 單糖： 結(jié)構(gòu)：鏈?zhǔn)?、環(huán)式； 物理性質(zhì)：溶解度、吸濕性、結(jié)晶性、粘度等 化學(xué)性質(zhì)：堿、酸、氧化還原作用、糖的成苷 作用、酯化和醚化、非酶褐變（要素）、焦糖化。 葡萄糖、果糖 3 低聚糖： 性質(zhì)：褐變、發(fā)酵、粘度等 蔗糖、麥芽糖和異麥芽糖、乳糖、海藻糖、棉籽糖、纖維二糖。 功能性低聚糖：低聚果糖、低聚木糖、低聚異麥芽糖、大豆低聚糖、低聚半乳糖、甲殼低聚糖、環(huán)狀低聚糖4 多糖： 性質(zhì)：溶解性、粘度（假塑性和觸變性）和穩(wěn)定性、凝膠、水解、風(fēng)味結(jié)合功能。 淀粉：結(jié)構(gòu)、糊化、老化、水解（高果糖玉米糖漿、葡萄糖當(dāng)量）、改

13、性、預(yù)糊化 纖維素：羧甲基、甲基、羥丙基甲基纖維素。 海藻膠：海藻多糖、卡拉膠、瓊脂 植物多糖：果膠、瓜兒膠、刺槐豆膠、魔芋葡甘露聚糖、阿拉伯膠。 微生物多糖：黃原膠、膳食纖維。作業(yè) Maillard反應(yīng)的基本因素和反應(yīng)機(jī)理？影響Maillard反應(yīng)的因素有哪些？如何控制Maillard反應(yīng)形成良好的色澤和風(fēng)味？F Maillard reaction美拉德反應(yīng): reaction between reducing sugars, mainly D-glucose, and a free amino acid or a free amino group of an amino acid that

14、 is part of a protein chain.Three primary elements: nitrogen-containing compounds, reducing sugars, and water. Characters: producing flavor and color. Desirable: milk chocolate flavor, candy flavor; Undesirable: nutrition loss, noxious, and mutagenesis materialCondign condition of Maillard reaction促

15、進(jìn)條件D-xyloseL-arabic gumhexosedisaccharide D-fructoseD-glucose Middling water contentpH 7.89.2Metal ion：Cu and Fe are accelerant, Fe+3Fe+2Restrain method of Maillard reaction抑制條件Dilution or reduce water content Lower pH Low temperatureAccede to glucose transform enzymeAccede to reducing agent (sulfit

16、e) before pigment forming. F Lactose intolerance: 乳糖不耐癥the ingested lactose is only partially hydrolyzed, or is not hydrolyzed at all.Deficiency of lactase result in lactose remaining in the lumen of the small intestine, producing abdominal distention and cramps.乳糖不耐癥：某種原因，攝入的乳糖僅部分水解，即部分被消化，或不是全部水解如

17、果缺少乳糖酶，乳糖保留在小腸腸腔內(nèi)，由于滲透作用，乳糖有將液體引向腸腔的趨勢，這種液體會產(chǎn)生腹脹和痙攣。Two ways to overcome lactose intoleranceRemove the lactose by fermentation.Reduce lactose by adding lactase to it.Lactose 乳糖- pyranose galactose combined with D-pyranose glucose by-1,4 glycoside.F 特證：white or light yellow crystal;F low solubility;F

18、 tiny sweet (1/6 of sucrose);F reducing sugar;F cow milk: 4.6-5.0%, human milk: 5-7%.F 作用：Lactose stimulates intestinal adsorption and retention of calciumF D-glucose and D-galactose are rapidly absorbed and enter the blood stream作業(yè) What is starch gelatinization and retrogradation? Which factors are

19、 related to starch gelatinization? How to prevent starch retrogradation? 淀粉的糊化和回生是什么？哪些因素對淀粉糊化有關(guān)嗎？如何防止淀粉回生嗎？Starches Gelatinization淀粉的糊化the disruption of molecular order within granules, irreversible granule swelling, loss of birefringence, loss of crystallinity, loss of polarized light cross, most

20、amylose dissolution in solution, viscosity increase, and starch granule cracking. 糊化：加熱破壞了結(jié)晶膠束區(qū)弱的氫鍵后，分子中的有序排列破壞，淀粉顆粒開始水合和吸水膨脹，雙折射消失，結(jié)晶區(qū)消失，偏振光十字消失，大部分直鏈淀粉溶解到溶液中，溶液黏度增加，淀粉顆粒破裂F Factors dependence :structure : amyloseamylopectinwater activity:；salts:alkalinityacidity: pH=10 Amylase:結(jié)構(gòu)，直鏈淀粉小于支鏈淀粉。水分活度，水

21、分活度高的淀粉糊化程度高。糖類，高濃度的糖水分子，使淀粉糊化受到抑制。鹽類，高濃度的鹽使淀粉糊化受到抑制，低濃度的鹽存在對糊化幾乎沒有影響酸堿度，pH<4時，淀粉水解為糊精，粘度降低；4<pH<7時，幾乎沒有影響；pH=10時，糊化速度會迅速加快。淀粉酶，淀粉酶活性高，會降低最高黏度，使得淀粉糊化速度加快。F Starch Retrogradation淀粉的老化As starch pastes are cooled and stored, the starch becomes progressively less soluble. Linear molecules assoc

22、iation and arrangement newly, starch molecules will precipitate. P198,27淀粉的老化：當(dāng)?shù)矸酆鋮s和貯藏時，淀粉溶解度逐步減小，減小過程中線性分子發(fā)生了重新締合排列，糊化的淀粉形成了沉淀或凝膠的過程。F Dependence factors: P198,913the molecular ratio and structures of amylose to amylopectin, amylose undergoing retrogardation at a much more rapid rate than does amy

23、lopectinwater content: 30%-60% temperature: 2-4 surfactant: presence and concentration of other ingredientsalkalinityacidity: 4<pH<10淀粉的種類，直鏈淀粉由于其空間三維網(wǎng)狀分布，相對支鏈淀粉易使微晶束氫鍵生成，一般比較易老化，直鏈淀粉含量愈多，老化愈快。老化后的淀粉與水失去親和力，并且難以被淀粉酶水解，不易被人體消化吸收。含水量，淀粉含水量為30%-60%時較易老化，含水量小于10%或大于60%時則不易老化。溫度，最適宜溫度在2-4，大于60或小于-2

24、0都不易發(fā)生老化。因此在速凍熟面制品時，要使其快速通過易老化的溫度區(qū)，并且在-18以下貯藏表面活性劑，蒸餾單甘酯與直鏈淀粉形成穩(wěn)定的復(fù)合物，會抑制淀粉的老化。酸堿度，食品在偏酸（pH4以下）或偏堿的條件下，不易老化F Staling of crumb: increase in firmness and a loss in freshness. Reason: gradual transition of amorphous starch to a partially crystalline. Polar lipids, GMP and SSL, retard crumb firming.原因：淀

25、粉的無定形部分轉(zhuǎn)變成結(jié)晶的老化狀態(tài)。實(shí)際上在烘焙結(jié)束冷卻時，老化已開始。當(dāng)烘焙食品冷卻到室溫時，直鏈淀粉大部分已老化了，而支鏈淀粉的老化則需較長時間才能完成，支鏈淀粉的老化是由支鏈締合引起的極性脂類能夠和淀粉形成直鏈淀粉-脂的絡(luò)合物，改變淀粉糊的流變性質(zhì)以及抑制淀粉分子的結(jié)晶，最終推遲了淀粉的老化。因此，將具有表面活性的極性脂如甘油棕櫚酸一酯（GMP）、其他的甘油一酯及其衍生物以及硬脂酰乳酰乳酸鈉（SSL）添加到面包中，可以延遲面包心變硬，延長貨架壽命。面包老化表現(xiàn)在面包心變硬，面包新鮮程度下降。F Dextrose equivalency (DE): reducing sugar as a

26、percentage of the solids. 淀粉的水解程度用DE表示，DE是葡萄糖當(dāng)量，用來衡量淀粉轉(zhuǎn)化為D-葡萄糖的程度。定義：還原糖（按葡萄糖計）占干物質(zhì)的百分比第5章 蛋白質(zhì)1 蛋白質(zhì)的組成、分類、一般性質(zhì)、化學(xué)性質(zhì)2 蛋白質(zhì)的結(jié)構(gòu)體系：四個結(jié)構(gòu)體系的骨架、肽鍵；穩(wěn)定蛋白質(zhì)結(jié)構(gòu)的作用力3.蛋白質(zhì)的變性F Protein Denaturation蛋白質(zhì)變性Denaturation: major changes in the secondary, tertiary, and quaternary structures without cleavage of backbone pept

27、ide bonds. 蛋白質(zhì)的二級、三級和四級結(jié)構(gòu)上的重大變化，但不涉及主鏈上肽鏈的斷裂。 F 變性因素的八個，對蛋白質(zhì)的影響理解F Tm or Td: temperature at the transition midpoint where the concentration ratio of native and denatured states is 1.Tm4080 P356,2835熔化溫度Tm或變性溫度Td：是指當(dāng)一個蛋白質(zhì)溶液被逐漸加熱并超過一個臨界溫度時，蛋白質(zhì)開始從天然狀態(tài)轉(zhuǎn)變?yōu)樽冃誀顟B(tài)，在這個轉(zhuǎn)變中點(diǎn)的溫度就稱為熔化溫度或變性溫度，在此溫度下蛋白質(zhì)的天然和變性狀態(tài)的濃度之比

28、為1。 4.蛋白質(zhì)的功能性質(zhì)Functional properties of Protein蛋白質(zhì)的功能性質(zhì) 概念those physical and chemical properties which affect the behavior of proteins in food systems during processing, storage, preparation and consumption.是指在食品加工、保藏、制備和消費(fèi)過程中影響蛋白質(zhì)在食品體系中的性能的蛋白質(zhì)的物理和化學(xué)性質(zhì)。例如：乳制品蛋白質(zhì)的功能性質(zhì)：乳化、黏度、發(fā)泡、膠凝、凝結(jié)、對脂肪的保留。肉制品中乳化、膠凝、內(nèi)

29、聚力、對水和脂肪的吸收和保持等。Size, shape, amino acid composition and sequence, net charge and distribution of charges, hydrophobicity/hydrophilicity ratio, etc. P365,3540決定功能性質(zhì)的物化性質(zhì)包括：大?。恍螤?；氨基酸組成和順序；凈電荷和電荷的分布；疏水性和親水性之比；二級、三級和四級結(jié)構(gòu)；分子柔性和剛性；分子間相互作用和同其它組分作用的能力。 水合性質(zhì)（影響因素）Definition of hydration capacitydefined as gr

30、ams of water bound per gram of protein when a dry protein powder is equilibrated with water vapor at 9095% relative humidity. P367,1314水合能力的定義：當(dāng)干蛋白質(zhì)粉與相對濕度為90-95%的水蒸汽達(dá)到平衡時，每克蛋白質(zhì)所結(jié)合的水的克數(shù)定義為蛋白質(zhì)結(jié)合水的能力界面性質(zhì)：乳化、起泡 interfacial properties of proteins界面性質(zhì)Concept: proteins migrate spontaneously to an air-water

31、 interface or an oil-water interface. 是指蛋白質(zhì)能自發(fā)地遷移至氣-水界面或油-水界面的性質(zhì)。蛋白質(zhì)在界面區(qū)域的濃度總是高于體相。Three attributes: (a) ability to rapidly adsorb to an interface; (b) ability to rapidly unfold and reorient at an interface; (c) ability to form film that withstand thermal and mechanical motions. 影響乳化因素，對乳化的影響Foaming Properties Concept: refers to its