【作者】 孟宗；

【导师】 王兴国；

【作者基本信息】 江南大学 ， 粮食、油脂及植物蛋白工程， 2011， 博士

【摘要】 牛油基塑性脂肪产品具有理想的塑性温度范围,便于实际应用,同时经高温烘焙后具有典型的风味,留香持久。基于上述优点,其在烘焙型脂肪中占有大量份额。但由于牛油本身甘油三酯（TAG）组成及结晶上的缺陷,使得牛油基塑性脂肪产品中很容易出现砂粒晶体,破坏产品柔软延展的特性。本文围绕牛油基塑性脂肪产品起砂机制及抑制开展研究,在对劣化全牛油基起酥油中砂粒晶体进行分子组成、结晶行为表征的基础上,动态分析了砂粒晶体形成过程中油脂迁移及晶型衍变规律,推测砂粒晶体的形成机制,指导牛油酯交换改性及添加乳化剂改善牛油分子组成和结晶特性,抑制砂粒晶体的产生。通过对劣化全牛油基起酥油中砂粒晶体和无砂晶体的对比研究,发现高熔点TAG如S₃（PPP、PPS、PSS和SSS）,S₂U（POS和SOS）在砂粒晶体中聚集,而低熔点S₂U和SU₂,如POP、SOO/SSL、PLO和POO则在无砂晶体中聚集,同时砂粒晶体中晶型已部分转化为β型。pNMR及振动流变结晶动力学分析都表明砂粒晶体部分结晶速率较慢,PLM晶体形态分析表明其在结晶过程中晶体聚集明显,形成的晶体束尺寸更大。在二种储存条件:①恒温（5℃和20℃）;②温度波动（5℃12 h 20℃12 h为一周期温度往复）下诱导实验室自制全牛油基模型起酥油（BTMS）起砂,同时以全棕榈油基模型起酥油（POMS）作为对照,对砂粒晶体形成过程中的脂肪晶体迁移聚集、晶型衍变,人体感官分析进行了系统评价,发现无论是BTMS还是POMS,在温度波动储存条件下晶体的生长、分级聚集过程更为迅速。相比恒温储存,波动储存更容易诱导砂粒晶体形成,且晶型β转化的速率更快。综合晶体尺寸及感官评定分析结果,推导出人体对塑性脂肪砂粒晶体感官的临界晶体尺寸范围为40-90μm,大于此范围的晶体人体通过感官评定很容易感知,而更小尺寸的晶体只有在高晶体浓度时才能被人体感知。将BTMS和POMS置于温度波动条件下继续储存至6个月,挑出其中的砂粒晶体和无砂晶体进行脂肪结晶网络各级结构层次对比分析表明:无论是BTMS还是在POMS中,高熔点TAG,如BTMS中S₃（SSS、PSS、PPS和PPP）,S₂U（SOS和POS）;POMS中S₃（PPP）,S₂U（POP和POS）,在砂粒晶体中发生聚集,含量偏高,部分β′晶型转变为β晶型,TAG的二倍链长堆积部分转化为三倍链长堆积,形成β′,β二倍链长和三倍链长的混合结晶体,动力学分析表明其结晶速率较慢。由此推测塑性脂肪起砂机制为:在结晶初始阶段,高熔点S₃作为种晶首先结晶,形成β′二倍链长型晶核,在温度波动提供驱动力的情况下,S₂U附着在晶核表面,促进晶核晶体的生长;晶体经进一步熟化后,球晶体数目增多,单个晶体的尺寸增大,结晶网络进一步密集化,其中S₃和S₂U成为球晶的晶体骨架组份,而绝大部分SU₂和U₃都被排除在颗粒晶体周围;同时,伴随着部分β′二倍链长型晶体向同时含β′与β晶型,TAG二倍链长和三倍链长堆积方式共存的复杂混合晶体转变,晶体间通过范德华作用力相互作用,发生进一步的聚集及生长,形成大的晶体束;最终,当晶体束的微结构尺寸超过了人的感官临界范围（40-90μm）,即表现为可被人体物理测定（手指间揉搓或口中融化砂粒般口感）,破坏产品感官和功能特性的砂粒晶体。采用低芥酸菜籽油作为不饱和脂肪供体,对牛油进行化学酯交换改性。根据最短时间SFC变化最大的原则,得到优化的反应条件:CH₃ONa用量0.4%,反应温度60 oC,反应时间30 min。经酯交换后,U₃,S₃和部分S₂U的含量降低,TAG组成更均匀,相容性更理想,避免熔点差异较大TAG间的迁移聚集和分级结晶。由于乳化剂脂肪酸酰基链与脂肪TAG酰基链间的酰基—酰基相互作用及大分子尺寸乳化剂的空间位阻效应,1%的乳化剂（分子蒸馏单甘酯、大豆卵磷脂、P-170、S-170、斯潘65、斯潘60）能有效控制含10%-40%低芥酸菜籽油的牛油酯交油的晶体尺寸,样品在温度波动储存6个月后最大晶体尺寸仍小于50μm,并保持二倍链长β′型结构,感官评定无砂粒晶体。由此可见,通过配比适量的植物油进行酯交换改性,结合适宜的乳化剂控制脂肪结晶,能够提高牛油基塑性脂肪产品的晶体稳定性,提高其对温度波动的耐受性,抑制砂粒晶体的形成。更多还原

【Abstract】 Beef tallow （BT）-based plastic fat products account for a large number of shares in baking fats due to its advantageous properties, such as ideal plasticity temperature range, ease of practical application, and typical aroma after baking, lasting fragrance. However, due to the triglyceride （TAG） composition and crystallization defect of BT, BT-based plastic fat products is prone to form granular crystals, which impair the consistency and plasticity of fat products. This research focuses on granular crystal formation mechanisms in plastic fats, and its inhibits. Based on characterize the TAG composition and crystallization behavior of the degradation all BT-based shortening, dynamic analysis the law of oil migration and polymorphism transformation during the formation of granular crystals, suggesting that the formation mechanism of granular crystals in plastic fats. Guide the BT interesterification modification and add the emulsifier to improve its molecular composition and crystalline properties, inhibit the formation of granular crystals.Through the comparative study of granular crystals and their surrounding materials separated from the degradation all BT-based shortening, it found that high melting point TAGs, such as S₃ （PPP, PPS, PSS and SSS）, S₂U （POS and SOS） occurred aggregation in the granular crystals, while the low melting point S₂U and SU₂, such as POP, SOO/SSL, PLO and POO were gathered in surrounding materials, sometims, granular crystals partially transformed intoβ-typ. pNMR and oscillatory rheology crystallization kinetic analysis indicated that the crystallization rate of granular crystal parts was slow, PLM analysis also showed that the granular crystal parts gathered obviously to form larger size crystal during the crystallization process.The granular crystals in BT-based shortenings （BTMS） were induced under two storage conditions:①constant temperature （5℃and 20℃, repectively）;②temperature fluctuations （5℃12 h 20℃12 h for a cycle）, while the palm oil-based shortenings （POMS） as the control. The fat crystal migration and aggregation, polymorphism evolution, human sensory evaluations during the formation of granular crystals were investigated systematically. It compared to the constant temperature storage, the crystal growth, hierarchical aggregation process was more quickly under temperature fluctuation conditions, and easier to induce the formation of granular crystals, sometimes, theβ-typ crystal conversion rate was faster in both BTMS or POMS. Comprehensive analysis of crystal size and the sensory evaluation results, derived that the sense critical crystal size range of the human body to plastic fats is 40-90μm, human perception through sensory evaluation is very easy if the crystal is larger than this range, and only the smaller size of the crystals in high concentrations can be perceived by the body. BTMS and POMS will be continue stored under the temperature fluctuation conditions to 6 months, and then comparative analysis the granular crystals and their surrounding materials following the structure hierarchy of fat crystal networks. It was found that the migration and aggregation of higher-melting TAGs, such as S₃ （SSS, PSS, PPS and PPP）, S₂U （SOS and POS） in BTMS, S₃ （PPP）, S₂U （POP and POS） in POMS, and consequently, polymorphic transformation fromβ′form of double chain length structures to complicated crystal structures, in which concurrently comprising theβandβ′form crystals of triple chain length and double chain length structures had occurred in granular crystals and its crystallization rate was slower, whether in BTMS or in POMS.The results suggested that the mechanism of granular crystal formation in plastic fats: in the initial stages of crystallization, high melting point S₃ TAG as the seed crystal, form the double chain lengthβ′-typ nuclei and crystallized firstly in the plastic fat system. S₂U TAG attached to the nucleus surface promoting the growth of crystal nuclei in the case of the driving force provided by the temperature fluctuation; After further aging, the number of spherulitic crystal and the size of a single crystal increase, crystalline network to further intensification, including S₃, S₂U TAGs become crystal backbone components, and most of SU₂, U₃ TAG are excluded from the crystal; At the same time, accompanied by part ofβ′crystal of double chain length structure transform to the complex crystal comprising theβandβ′form crystals of triple chain length and double chain length structures of TAG stacking, crystals further aggregate and grow, form large crystal clusters; The microstructure size of these crystal aggregates exceeded the sensory threshold （40-90μm）, and the aggregates could be detected upon visual and physical examination （by rubbing in between the fingers or melting in the mouth） and therefore impaired the sensory and functional properties of the finished products.Canola oil as the unsaturated fat donor, modify BT by chemical interesterification （CIE）. According to the principle of the shortest time achieve the greatest change in SFC get the optimal reaction conditions: 0.4% CH₃ONa, reaction temperature 60 oC, reaction time 30 minimums. After CIE, U₃, S₃, and part of the S₂U TAGs lower, making the TAG of interesterified blends more uniform, while compatibility even better, to avoid migration, aggregation and fractional crystallization between the large differences melting TAGs. 1% emulsifier （molecular distilled monoglycerides, soy lecithin, P-170, S-170, Span 65, Span 60） can effectively control the crystal size of interesterified blends containing 10%-40% canola oil as the acyl-acyl interaction between fatty acyl chains of emulsifier and fatty acyl chains of TAGs, and steric effect of emulsifier macromolecular size. After 6 months’temperature fluctuation storage, the maximum crystal size of sample is still smaller than 50μm, while maintainingβ′crystal of the double chain length structures, and the sensory evaluation have no granular crystals. Thus, interesterified with an amount of vegetable oil, and combined with suitable emulsifiers to control the fat crystallization, which can increase crystal stability of BT-based plastic products, also can increase their tolerance to temperature fluctuations and inhibit the formation of granular crystals.更多还原