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    • The electronic nose was also used to

    2018-11-09

    The electronic nose was also used to measure the shrimp freshness [18–22], the result showed that the electronic nose could detect the odor change of shrimp. Most application of electronic nose focused on pattern recognition techniques [19–26]. Principal component analysis (PCA) was a pattern recognition technique which was often used to reduce the dimensionality of a data set while retaining as much information as possible, employed with tin oxide gas BV6 arrays [23]. PCA scores was plotted to demonstrate the separation achieved but no classification algorithm was tried [26], it was inconvenience for predicting unknown samples. The purpose of this study is to construct a model to predict freshness of shrimp; firstly, the principal component was obtained, secondly, Fisher Liner Discriminant was employed to establish a model with the principal component above, and then the freshness of shrimp was predicted with the model.
    Materials and method
    Results
    Discussions Sensory scores showed decline with storage time, it was consistent with sensory evaluation, which was obtained from appearance, odors, and texture of shrimp, for frozen shrimp performed by Theofania Tsironi et al. [4]. It showed that shrimp was unacceptable after storage for 4day, however, it was for 5day, shrimp stored at 4°C reported by Tang et al. [19]. It was not performed by Li et al. [20]. TVBN value, shrimp stored at 5°C for 1day, was 12.88mg/100g, it was similar to the TVBN value 12.19mg/100g, stored at 4°C for 1day reported by Ash Hocao ğlu et al. [9]; It was 22.39mg/100g after storage for 4day, lower than 31.25mg/100g performed by Li et al. [20], close to 24.82mg/100g reported by Tang et al. [19], shrimp stored at 4°C. After storage for 5days, it was 30.74mg/100g, exceeding acceptable limits (National Standard of the People\'s Republic of China, GB2733-2005, 2005). PCA was often used while electronic nose evaluating the shrimp freshness. PCA scores were plotted to show the separate effect of different shrimp. Tang et al. [19] reported that the odor of shrimp, stored at 4°C for 6days, was detected by PEN3 electronic nose, the freshness of shrimp was classified to 3 grading according to sensory evaluation and TVBN value, and The 3 grading was better discriminated in PCA scores scheme. Zhao et al. [21] reported that the odor of head and flesh of shrimp, stored at 0°C for 10day, was respectively detected by PEN3 electronic nose, PCA scores scheme showed that the odor of shrimp, storage for different time, was distinguished. Similar result was reported by Li et al. [20]. Chai et al. [18] also reported that the odor of shrimp, respectively stored at 4°C for 5days, −10°C for 20days, and −15°C for 60days was detected by self-made electronic nose, the feature of output signal was extracted, and the effect of storage temperature and time on the feature extracted was studied. These PCA score schemes demonstrated that the separation achievedwas inconvenient for predicting unknown freshness of shrimp. In this paper, the temperature and humidity were controlled to minimize the effect of temperature and humidity on signal of sensor during measurement, this was not mentioned in these report [19–22]. The PCA was used to reduce the dimensionality, three principal component scores were obtained and used to build a model to predict the freshness of shrimp with Fisher Liner Discriminant. The result was better, and the discriminant rates were 98.3% for 120 modeling sample data, and 91.7% for 36 testing sample data. This model was conveniently applied to estimate the shrimp freshness.
    Conclusions The sensory evaluation and the content of TVBN were performed to indicate the freshness of the shrimp. Sensory scores showed decline with storage time, and the shrimp was unacceptable after storage for 4days. TVBN value increased with storage time. When the shrimp was stored five days later at 5°C, it was 30.74mg/100g, exceeding acceptable limits (National Standard of the People\'s Republic of China, GB2733-2005, 2005), and the shrimp was rotten and inedible.