啤酒新鲜度是市场消费者非常关注的品质指标, 也是各大啤酒公司的核心竞争力。 传统啤酒新鲜度检测方法一般需要十分昂贵的分析仪器和化学试剂, 消耗大量时间, 检测成本较高。 随着啤酒的老化, 啤酒中的成分物质亦将发生变化, 其对应的光谱特征也将发生改变。 利用光谱分析技术, 挖掘表征啤酒老化的光谱特征, 构建啤酒新鲜度指数(BFI), 可实现啤酒新鲜度的快速、 无损检测。 将新鲜啤酒分三等份装入相同容器, 其中2份为避光保存, 1份为光照下保存, 用PSR-3500光谱仪对啤酒样品进行光谱采集, 每隔24 h采集一次, 共采集6次, 获得不同新鲜程度啤酒的光谱数据。 对采集的光谱数据进行特征波段选择、 包络线去除等预处理, 增强后的光谱显示842.0 nm处的波谷深度随放置时间的增长而变小, 因此基于842.0 nm的波谷深度构建反应啤酒新鲜度的光谱特征指数(BFI)。 实验结果表明, BFI值随放置时间的增长而逐渐下降, 且避光保存的两组样品BFI值下降速率基本一致, 而由于光照加速了啤酒中的老化反应, 使得光照保存的样品BFI值下降速率较快, 结果显示BFI能够较好指示啤酒的新鲜程度。 此外, 通过模拟不同光谱分辨率与信噪比水平, 评价BFI对光谱检测设备性能的敏感性。 具体地, 利用高斯函数分布函数和平均分布函数分别生成光谱分辨率为5~40 nm的数据和信噪比为10~60 dB的数据, 对其进行特征波段选择、 包络线去除等预处理, 计算BFI值并进行分析。 实验显示, 当光谱分辨率低于15 nm、 信噪比低于10 dB时, 样品842.0 nm的光谱吸收特征逐渐被掩盖, BFI将难以指示啤酒的新鲜程度。 然而, 只要在798~872 nm及附近波段光谱分辨率优于10 nm、 信噪比不低于35 dB, BFI即可准确指示啤酒新鲜度, BFI对光谱仪的性能要求并不严苛。 综上所述, BFI能够准确指示啤酒新鲜度, 服务于便携式啤酒新鲜度光谱检测设备的设计与研发, 促进光谱分析技术在啤酒品质无损检测及相关领域的应用推广。

Traditional beer freshness detection methods usually need very expensive analytical instruments and chemical reagents, which consume a lot of time and cost a lot. In this paper, spectral analysis technology is used to explore the Beer Fresh Index (BFI), which can detect the agree of beer freshness rapidly and non-destructively. Specifically, the spectrum of beer samples was collected by PSR-3500 spectrometer every 24 hours. Then, the spectral data were processed by band selection and continuum removal. The enhanced spectra showed that the depth at 842.0 nm was decreased with the increase of storage time. Therefore, the characteristic spectral index (BFI) of beer freshness was constructed based on the depth at 842.0 nm. The experimental results show that BFI value decreases gradually with the increase of storage time, which can indicate the freshness of beer well. In addition, the sensitivity of BFI to the spectral equipment was evaluated by simulating different spectral resolution and signal-to-noise ratio levels. Specifically, the data with a spectral resolution of 5~40 nm and signal-to-noise ratio of 10~60 dB are generated by using the Gauss function distribution function and the average distribution function respectively and the BFI values are calculated and analyzed. Experiments show that when the spectral resolution is less than 15 nm and the signal-to-noise ratio is less than 10 dB, the absorption feature of 842.0 nm in the spectrum are gradually concealed, and BFI is difficult to indicate the freshness of beer. However, as long as the spectral resolution is better than 10 nm and the signal-to-noise ratio is not less than 35 dB in 798~872 nm, BFI can accurately indicate the freshness of beer. The requirements of BFI for the spectrometer are not strict. To sum up, the BFI proposed in this study can accurately indicate beer freshness, serve the design of portable beer freshness equipment, and promote the application of spectral analysis technology in non-destructive detection of beer quality.