Abstract The effect of heat treatment on tryptophan front-face fluorescence emission spectra of reconstituted skim milk was assessed. Samples were heat-treated from 70 to 100 °C at six holding times. Treating milk at 90 and 100 °C induced a decrease in fluorescence intensity (∼37 and ∼47 %) and a red shift (12 and 14 nm), respectively, with both parameters significantly affected at 99.9 % by temperature, time, and the interaction of both factors. Red shift, which could be attributed to whey protein denaturation and tryptophan exposure to increasing solvent polarity, was found to follow a quadratic trend as a function of holding time (from 0 to 60 min). The decrease of fluorescence intensity observed at those two temperatures and in the mentioned holding time range was also a quadratic function of the associated red shift. Emission intensity change at a single wavelength (∼340 nm) was partly caused by direct intensity decrease and indirectly due to the emission maximum shift. Tryptophan fluorescence allowed sample classification by PCA analysis according to heat load, i.e., temperature and time. These results established the bases for development of a cost-effective sensor based on simple, economic optical components for measurement of a few well-selected emission wavelengths, which associated with data processing, should allow inline control of milk heat treatment.

中文翻译：

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热处理对脱脂乳中色氨酸正面荧光光谱的影响

摘要 评估了热处理对复原脱脂乳色氨酸正面荧光发射光谱的影响。样品在 70 至 100 °C 之间进行了六次保温处理。在 90 和 100 °C 下处理牛奶分别导致荧光强度降低（~37% 和~47%）和红移（12 和 14 nm），这两个参数受温度、时间和温度的显着影响为 99.9%。两个因素的相互作用。红移可归因于乳清蛋白变性和色氨酸暴露于增加的溶剂极性，被发现遵循作为保持时间（从 0 到 60 分钟）函数的二次趋势。在这两个温度和上述保持时间范围内观察到的荧光强度降低也是相关红移的二次函数。单个波长（~340 nm）的发射强度变化部分是由直接强度降低引起的，部分是由于发射最大偏移引起的。色氨酸荧光允许根据热负荷（即温度和时间）通过 PCA 分析对样品进行分类。这些结果为基于简单、经济的光学元件开发具有成本效益的传感器奠定了基础，用于测量与数据处理相关的几个精心挑选的发射波长，应该允许对牛奶热处理进行在线控制。