Cereals are a grain or edible seed which produced by grass family that rich in essential nutrition for human and some animals. Several cereal products are consumed widely in the word i.e rice, wheat, maize or corn, barley, oats, rye, millet, and sorghum, and grown nearly 60% of cultivated land in the world. The chemical composition of cereal grains is characterized by the high content of carbohydrates mainly in starch (56-74%), a moderate content of protein (8-11%) and a minor content of lipids (2-4%) and mineral (1-35) (Kohler & Wieser, 2013). Many experimental pieces of evidence also present a range of substance which may have benefits to human health in some cereals product which referred to phytochemicals or bioactive compound substances.
Phytochemicals are a secondary metabolite of several plants (Yao et al, 2004), and play an important role in human health even though not classified as essential nutrients (Temple, 2000). Phytochemical compounds include (1) non-nutrient carotenoids, (2) compounds which containing phenol rings (phenolic compounds) and flavonoid, (3) plant-derivates estrogens (phytoestrogens), and (4) a group of sulfur compounds (glucosinolates) (Johnson & Williamson, 2000). These compounds have been proved as antiradical scavenging and antioxidant which closely related to chronic diseases (Tiwari & Cummins, 2013).Naturally, phytochemicals in the plant are responsible for color, flavor, and odor (Miglio et al., 2008), the availability and the content are influenced by crop type, variety, environmental condition, cultivar location, germination, processing and storage (Escribano-Bailon, 2004; Carbone et al., 2011).
Whole grains contain some important phytochemical compounds such as a phenolic compound, carotenoid, phytic acid, phytosterols, tocol, gamma-oryzanol and beta-glucan (Gani et al., 2012). Phenolic compounds are the most abundant and has capability as a prevention agent of cancer and cardiovascular disease (Yao et al., 2004). This health benefits of polyphenols are closely related to their chemical structure that characterized by phenol and at least one hydroxyl group. According to the chemical structure, there are 5 major families of polyphenols: phenolic acids, flavonoids, lignans, stilbenes and curcuminoids (Panickar & Anderson, 2011).
Many experiments present the availability of phenolic acid and flavonoid (anthocyanins, flavone, flavonol, isoflavone) in cereal product. Whole rice that the color ranged from white to red and black (purple) contain of polyphenol that can be classified into three groups: (1) phenolic acid, (2) anthocyanins, mainly available in black or purple rice, and (3) proanthocyanidins such as catechin that found in red rice (Qiu et al., 2010; Gunaratne et al., 2013). Phenolic acid also can be found in wheat (Zhang et al., 2012) and the availability is influenced by genotype and agricultural factor (Gastonyi et al., 2011). Moreover, pigmented wheat also contain anthocyanin, a flavonoid substance that has antioxidant activities (Giardano et al., 2017), and winter wheat contain tritin substance (Moheb et al., 2013) as a methylated cereal flavone that plays an important role as anti-obesity agent (Lee et al.,2016). These experiment evidence have proven that whole grain contains unique and specific bioactive compound that complement those in fruits and vegetables when consuming together.
Recently, Identification and quantification of the phytochemical compound in cereal mainly divided into two steps, extraction and determination or analytical method. Optimized extraction is a significant importance to accurately quantify the phytochemical content in food and plant products. The conventional methods including soaking, stirring, distillation, manual mixing, and percolation have been used since several decades ago. In the recent decade, several new extraction technologies including microwave-assisted extraction, ultrasound-assisted extraction, pressurized liquid extraction, subcritical and supercritical fluid extraction, solid-phase extraction and enzyme assisted extraction have been used to obtain the higher yields of bioactive compounds (Luthria et al., 2015). Regarding analytical methods for determination, some methods and technologies have been used based on the research goal and resources availability. High-performance liquid chromatography (HPLC) and gas chromatography methods have been used for separation, identification, and quantification of the phytochemical component. These chemicals and physical techniques exhibit high accuracy and good reliability but have certain limitation such as high cost, time-consuming, and high skill operator requirement.
In recent years, several rapid and non-destructive techniques have been developed and applied to measure chemical component from agricultural and food product. These non-destructive testing technologies are rapid, accurate and reliable and simple to evaluate quality attribute that materials. This review provides an overview of an important phytochemical compound in cereal product such as phenolic acid and several flavonoids i.e. anthocyanins, flavone, flavonol, and isoflavone. For the comprehensive study, this review also present the recent method to quantify the component and the challenge to apply the non-destructive method for rapid, accurate and simple determination technique.