Granular Crystals Formation In Beef Tallow-based Plastic Fats-mechanisms And Inhibitions

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.