Hyperspectral imaging as a powerful tool for identification of papaya seeds in black pepper
Introduction
Spice market is valued at US$ 4 billion, with a growth forecast of US$ 6.5 billion in the near future (Jack, 2006). Therefore, the spices and herbs industry is constantly under threat, with spices of high economic value, such as saffron, black pepper, paprika, oregano, vanilla, turmeric and cinnamon, being more susceptible to adulteration (Galvin-King, Haughey, & Elliott, 2018).
Food adulteration is defined as the addition of exogenous components, substitution of their natural components or false information of the food composition (Barreto, Cruz-Tirado, Siche, & Quevedo, 2018). Since the most common form of consumption of herbs and spices is crushed or ground, they are susceptible to adulteration at any stage of their long and complex supply chain. In addition, there are groups of adulterants that can cause damage to the consumer's health (Lakshmi, 2012).
The main countries producing black pepper are Vietnam, Indonesia, Brazil, India and China (Zhu, Mojel, & Li, 2018), being India the largest exporting country. Black pepper (Piper nigrum L.) is one of the best-known species of the Piperaceae family and is widely grown in southern India and Sri Lanka (Vadivel et al., 2018), where it is known as 'Karuthaponnu' or 'black gold' (Bhattacharjee, Singhal, & Gholap, 2003). The main use of black pepper is as a spice and flavoring agent. However, it can also be used as anti-metastatic, antiapoptotic, antispermatogenic, antibacterial, anti-colon toxin, antidepressant, antifungal, antidiarrhoeal, insecticidal, antithyroid, anti-inflammatory, antimutagenic, antioxidative, antiriyretic, antispasmodic, antitumor, ciprofloxacin potentiator, gastric ailments, hepatoprotective, intermittent fever and larvicidal activity (Agbor et al., 2006, Ahmad et al., 2012, Vijayan and Thampuran, 2000). Its high demand makes it susceptible to adulteration by addition of starch, buckwheat or millet (McGoverin, September, Geladia, & Manley, 2012), papaya seeds (Dhanya, Syamkumar, & Sasikumar, 2009), chilli (Parvathy et al., 2014) and spent material and inferior production-own materials (Wilde, Haughey, Galvin-King, & Elliott, 2019).
Probably, papaya seeds (Carica papaya L.) are the most common adulterant, due to their physical similarities, low cost (residue) and easy availability (Dhanya et al., 2009, Pruthi and Kulkarni, 1969) (Fig. 1). The consequences for consumers’ health regarding the consumption of papaya seeds are not clear. Papaya seeds are used as a carminative, vermifuge, emmenagogue and counter-irritant (Vaidyaratnam, 1994), for controlling of diabetes mellitus, hypercholesterolemia and hypertension (Abo, Fred-Jaiyesimi, & Jaiyesimi, 2008) and the ripened seeds are taken with rice to treat diarrhea (Parrotta, 2001). However, it has also been reported that papaya seeds can cause liver and stomach problems (Lakshmi, 2012), and they have even been used as abortifacients (Vaidyaratnam, 1994), its detection is important to ensure the health of the consumer, in addition to its economic impact to customers. Nevertheless, although positive effects in consumer health are possible, the presence of papaya seeds in black pepper is considered food fraud.
Several methods have been developed to identify the presence of papaya seeds in black pepper in berries or powder. The first studies used microscopic examination (Pruthi and Kulkarni, 1969, TremlovÁ, 2001) and pepper seed staining using a potassium iodine/iodine solution (Madan et al., 1996, Sreedharan et al., 1981). Later, more sophisticated methods were used, as gas chromatography (GC) (Curl & Fenwick, 1983), sequence characterized amplified region (SCAR) for powder samples (Dhanya et al., 2009), thin layer Chromatography coupled with Mass Spectrometer (GC-MS) (Bhattacharjee et al., 2003, Paradkar et al., 2001) and Fluorescence and High Performance Liquid Chromatography (HPLC) (Jain et al., 2007, Vadivel et al., 2018). However, even though these methods prove to be efficient, they are often expensive and time consuming, require highly qualified staff, and usually destructive. Recently, Vadivel et al. (2018) showed the ability of Near Infrared Spectroscopy (NIRS) (900–1700 nm) to differentiate between pure papaya seeds and pure black pepper. Later, Wilde et al. (2019) achieved 90% and 100% correct classification for pure black pepper and black pepper adulterated with papaya seeds (10–40%), respectively, using NIRS.
Hyperspectral imaging system in the near infrared region (NIR-HSI), combines spectroscopy, which offers chemical information about the food, with imaging, providing spatial information related to the physical characteristics of shape and texture (Velásquez, Cruz-Tirado, Siche, & Quevedo, 2017). NIR-HSI has been quite efficient to determine adulterants in tea samples (Sandasi, Chen, Vermaak, & Viljoen, 2018) and black pepper (McGoverin et al., 2012), being a very promising technique for analysis of samples in powders (Su & Sun, 2018) and seeds (Huang, Tang, Yang, & Zhu, 2016).
The aim of this research was to develop a rapid method based on hyperspectral images for the identification of papaya seeds in black pepper in both powder and berries. To this end, spectral information from hyperspectral images and chemometrics were used to distinguish between black pepper and papaya seeds, and also to quantify the amount of ground papaya seeds added to black pepper.
Section snippets
Sample preparation
Samples of black pepper (BP) berries (Piper nigrum) from three suppliers were purchased from local markets (Trujillo, Peru). The samples were transported to the Agro-industrial Processes Engineering Laboratory of the National University of Trujillo (Trujillo, Peru), where the grains with defects were discarded and then stored at room temperature (∼25 °C). Papaya (Carica papaya L.) seeds (PS) were collected from different local producers from Trujillo (Peru) and transported to the laboratory,
Spectral features of the adulterated samples
The spectra of the relative absorbance (previously smoothing) of black pepper, papaya seeds and mixtures are represented in Fig. 2A. The black pepper spectra presented absorbance values higher than papaya seeds, although with a similar absorbance pattern. Similar NIR spectral pattern for pure black pepper and pure papaya seeds were reported by Wilde et al. (2019). Both the black pepper and papaya seeds had absorption at approximately 1200–1400 nm, corresponding to second overtone of CH and
Conclusions
Our research demonstrated that NIR-HSI is capable to detect papaya seeds in pure black pepper, in berries and powder samples. SIMCA classification allowed to identify and to classify berries and powder black pepper, papaya seeds and mixtures with sensitivity higher than 90% and error rate less than 8%. The PLS model performed with important wavelengths present a good predictive capability to predict papaya seeds concentration in black pepper powder samples. This pixel wise distribution of
Acknowledgement
Luis Jam Pier Cruz Tirado acknowledges São Paulo Research Foundation (FAPESP) for the scholarship project number 2018/02500-4. The authors appreciate the support of Professor Maria Angela de Almeida Meireles for reviewing the manuscript.
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These authors contributed equal work to this paper.