New York State Agricultural Experiment Station, Cornell Univ., Dept. of Food Science and Technology, 630 W. North St., Geneva, NY 14456, USA.
J Food Sci. 2010 Apr;75(3):C297-304. doi: 10.1111/j.1750-3841.2010.01559.x.
The disruption of plant cell walls during fruit juice processing results in the enzymatic formation of herbaceous-smelling green leaf volatiles (GLVs). Our objective was to assess the impact of thermal processing conditions on resulting levels of GLVs (hexanal, trans-2-hexenal, hexanol, cis-3-hexenol, and trans-2-hexenol), total phenols, monomeric anthocyanins, and percent polymeric color in Concord grape juice. The effects of fruit maturity and stage of juice processing on juice GLV content was also assessed. Of the GLVs studied, only trans-2-hexenal routinely exceeded its published sensory threshold in finished juice. We observed an inverse linear correlation between berry maturity (total soluble solids) and trans-2-hexenal levels in finished juice (P < 0.05, R(2)= 0.91). Trans-2-hexenal was at a maximum immediately following crushing (569 microg/kg, >30-fold over detection threshold [DT]), decreased to 100 microg/kg following depectinization, pressing, and pasteurization, and to 32 microg/kg following cold-stabilization. The loss of trans-2-hexenal could be explained primarily by its reduction to trans-2-hexenol, which increased from 53 microg/kg after crushing to 500 microg/kg after cold-stabilization. High temperature pretreatment of must immediately following crushing ("hot break") resulted in 5- to 6-fold higher concentrations of trans-2-hexenal in the final bottled juice as compared to conventional hot press. Contrary to expectations, no significant increase in phenolics and anthocyanins were observed in hot break conditions. These results indicate that hot break procedures may thermally inactivate enzymes responsible for transforming trans-2-hexenal under normal processing conditions and potentially alter the flavor qualities of the finished Concord juice. Different equivalent pasteurization regimes (82 to 93 degrees C) prior to bottling had no significant effect on GLV content of the finished Concord juices (P > 0.05).
Introducing new processing techniques to fruit juice production can potentially result in undesirable changes to organoleptic properties. We have observed significantly higher levels of trans-2-hexenal, a potent herbaceous off-flavor, in Concord grape juice prepared with an initial high temperature heat treatment ("hot break"). Concord juice producers should be cautious in using hot break processing, especially with immature fruit, as it may result in persistence of green aromas in juice.
在果汁加工过程中，植物细胞壁的破坏导致了草本气味的绿叶挥发物（GLV）的酶形成。我们的目的是评估热加工条件对 GLV（己醛、反式-2-己烯醛、己醇、顺-3-己烯醇和反式-2-己烯醇）、总酚、单体花青素和聚合色百分比的影响 Concord 葡萄汁。还评估了水果成熟度和果汁加工阶段对果汁 GLV 含量的影响。在所研究的 GLV 中，只有反式-2-己烯醛在成品果汁中经常超过其公布的感官阈值。我们观察到浆果成熟度（总可溶性固形物）与成品果汁中反式-2-己烯醛水平之间呈线性反比关系（P<0.05，R²=0.91）。反式-2-己烯醛在榨汁后立即达到最大值（569μg/kg，超过检测阈值[DT]30 倍），在去果胶化、压榨和巴氏杀菌后降至 100μg/kg，在冷稳定化后降至 32μg/kg。反式-2-己烯醛的损失主要可以解释为其转化为反式-2-己烯醇，反式-2-己烯醇在榨汁后从 53μg/kg 增加到冷稳定化后的 500μg/kg。压榨后立即对葡萄汁进行高温预处理（“热破”），与传统的热压榨相比，最终装瓶果汁中的反式-2-己烯醛浓度高 5-6 倍。与预期相反，在热破条件下没有观察到酚类和花青素的显著增加。这些结果表明，热破程序可能会使在正常加工条件下负责转化反式-2-己烯醛的酶失活，并可能改变成品 Concord 果汁的风味品质。装瓶前不同的等效巴氏杀菌（82 至 93°C）对成品 Concord 果汁的 GLV 含量没有显著影响（P>0.05）。
将新技术引入果汁生产可能会导致感官特性的不良变化。我们观察到在使用初始高温热处理（“热破”）制备 Concord 葡萄汁时，反式-2-己烯醛（一种强烈的草本气味）的含量显着升高。 Concord 果汁生产商在使用热破加工时应谨慎，尤其是在使用未成熟的水果时，因为这可能会导致果汁中持续存在青草香气。
