**2.1 Beetroot**

Beetroot (*B. vulgaris* subsp. *vulgaris* L.) (Family: Chenopodiaceae) also known as red beetroot has fleshy root that is commonly consumed in form of supplemental juice, powder, bread, gel, oven-dried, pickled, pureed or jam-processed across different food cultures. Its bioactive phytochemicals include phenolics and carotenoids, and betalains hydrosoluble nitrogen containing pigments (e.g., betacyanin that are red-violet and betaxanthin that are yellow-orange) [21]. Betalains form 70–100% of the total phenolics and have antioxidant and anti-inflammatory properties and anticarcinogenic potential [22]. Antiviral and antimicrobial effects of betalain pigments have also been reported [23]. Other antioxidant compounds include rutin, epicatechin, and caffeic acid. The sugar comprises mainly of sucrose (91.6%) [24], with a small and relatively similar proportion of glucose and fructose [25]. Red beetroot also contains dietary fiber, minerals (e.g., potassium, sodium, iron, copper, magnesium, calcium, phosphorus, and zinc), and vitamins (e.g., retinol, folate, ascorbic acid, and B-complex [26]. Moreover, beetroot contains a substantial amount of both nonessential and essential amino acids.

#### **2.2 Cassava**

Cassava (*M. esculenta* Crantz) (Family: Euphorbiaceae) is a starchy fibrous root crop used for traditional desserts, salad dressing, soup thickening, binding agent in sausages, high fructose syrup, and textile industries [27]. The sweet type of cassava root can be boiled or roasted and eaten as fresh root, or minimally processed into various products. Cassava contains alkaloids, as well as flavonoids that have antioxidant and hypolipidemic effects [28], and glycosides that are potent for heart disease [29]. It has low content of nutrients such as protein (<2%), fat (<0.2%), and fiber (<4%) [30]. Most of the carbohydrate is present as starch (>32% of fresh weight) with smaller amounts of free sugars (less than 1% of fresh weight). It has rich dry matter (>80%) thus making it a good source of energy [27]. The root also contains minimal amount of micronutrients (e.g., iron, potassium, magnesium, copper, zinc, and manganese. It also has some anti-nutrients and toxic substances (e.g., cyanogenic glucosides), which together with their breakdown products (cyanohydrins and free hydrocyanic acid [HCN]) that are formed during processing, can inhibit the digestibility and intake of major nutrients [31]. The yellow root varieties contain a significant concentration of β-carotene (up to 1 mg 100 g− 1,dry-weight) [32].

#### **2.3 Carrot**

Carrots (*D. carota* L.) (Family: Apiaceae [Umbelliferae]) play a major role in human nutrition, because of their high dietary value [33]. Phytochemicals present comprise mainly of phenolic compounds (e.g., phenolic acids, such as *p*-hydroxybenzoic, caffeic, and chlorogenic; and flavonoids such as anthocyanins), carotenoids (a precursor to vitamin A formation, which is involved in vision, cell differentiation, synthesis of glycoproteins, mucus secretion from the epithelial cells, and overall growth and development of bones) [34], polyacetylenes, and ascorbic acid. These chemicals aid in the risk reduction of cancer and cardiovascular diseases due to their antioxidant, anti-inflammatory, plasma lipid modification, and anti-tumor properties [35]. Phenolic acids are the potentially bitter compounds found in carrot peels. The moisture content of carrot varies from 86 to 89% [36]. They are good source of carbohydrates and minerals like calcium, phosphorus, iron, and magnesium, and also contain protein (0.9%), fat (0.2%), carbohydrate (10.6%), crude fiber (1.2%), and total ash (1.1%) [36].

#### **2.4 Radish**

Radish (*R. sativus* L.) (Family: Brassicaceae) has high nutritional value and is consumed in salads, or cooked or salted together with other vegetables. The roots can also be processed as dried or canned pickles. The extracts of radishes have been used to treat stomach disorders, urinary tract infections, hepatic inflammation, cardiac disorders, and ulcers [37]. Various reports have recorded the antimicrobial, anticancer, antioxidant, and anxiety reducing properties of radishes. Phytochemicals present in radish include alkaloids, reducing sugar, flavonoids, glycosides, cardiac glycosides, tannins, saponin, protein, amino acid, terpenoids, and steroids [38]. Anthocyanin pigments provide the red color of roots, while a high potential to form isothiocyanates contributes to the pungent flavor and distinctive taste [39]. Radish is low in calories but has a high content of vitamin C which helps to build tissue, blood vessels, bones and teeth. Other vitamins (e.g., B6 and folate) and minerals (e.g., potassium, magnesium, calcium, iron, zinc, copper, sodium, and phosphorous) are also found in radish roots. Also, radish has fiber and roughage that is effective in the treatment of constipation.

#### **2.5 Potato**

Potato (*S. tuberosum* L.) (Family: Solanaceae) is a staple food that is often cooked or processed into edible products such as fries and chips. It contains several phytochemicals such as phenolics, flavonoids, polyamines, and carotenoids. These phytochemicals have beneficial effects on human health hence they are highly desirable in diet. The phenolics, together with amino acids present in potatoes, confer anti-oxidant protection towards tissue damage, reactive oxygen species and diseases like atherosclerosis, diabetes mellitus, renal failure, and cancer [40]. Nutritionally,

potato has complex carbohydrates (>20%) in the form of free sugars (with glucose and fructose as the principal monosaccharides and sucrose as the major disaccharide, crude proteins (>2.5%), crude fats (0.1%), crude fiber (0.6%), vitamins, and water (74%) and along with minerals (>0.8%), amino acids, and trace elements that include potassium, sodium, iodine, and magnesium, folic acid, pyridoxine, vitamin C, and iron. Additionally, potatoes contain glycoalkaloids, which are toxic steroidal glycosides and anti-nutritional substances. Although they play a role in plant resistance to bacterial and fungal diseases and pests, when in excessive amounts, they worsen taste, and a concentration above 200 mg·kg−1 of fresh weight has toxic effects on the human body [41].

### **3. Pre-storage treatment of root vegetables**

Freshly harvested root vegetables are metabolically active, and therefore still undergoing the physiological and biological processes of senescence and maturation. The rates of these processes are influenced primarily by the produce temperature. To prolong postharvest nutritional and quality (e.g., appearance, texture, and flavor) attributes, freshly harvested produce is often exposed to one or several optimal prestorage treatments that often work by; slowing down the senescence and maturation processes, reducing/inhibiting development of physiological disorders and growth of decay producing microorganisms, restricting enzymatic and respiratory activity, inhibiting water loss, and reducing ethylene production. Physical treatments include; heat [42], irradiation [19], coatings [15], pre-cooling [18] and curing [43].

Heat treatment methods that have been applied on carrot and potato include hot-water (sometimes accompanied by brushing), hot dry air, and steam [44–46]. These treatments activate or deactivate enzymatic activities that result in reduced effects on the phytochemical and nutrient content, besides reducing chilling injuries and controlling decay. The treatments can be of short (up to 1 h) or long-term (up to 4 days) duration, but they have high energy costs. Gamma irradiation and short wave ultraviolet radiation have been used to effectively inhibit growth and development of sprouts and microbial pathogens on potato [47, 48]. However, their use is still subject to strict legislation. Paraffin wax coat is often used in combination with the exclusion of oxygen or submerging roots in water or storing in an anaerobic environment that can inhibit the streaking of the cassava xylem tissue [20, 49].

Pre-cooling is the removal of field heat in the produce immediately following harvest by using methods that include; Hydro-cooling (i.e., submerging crops in cold water), forced-air cooling (i.e., cold air is directed directly through the crop at high velocity), room cooling (i.e., placing crops in a cold room where cold air passing through a fan) and package icing (i.e., placing crushed ice directly on top of the produce). The choice of the method depends on the product type and factors such as the airflow rate, air, and produce temperature, relative humidity, and the packing configuration [50]. Bunched beetroots (with tops) are pre-cooled to optimal level of below 4°C within 4–6 h of harvest, while mature beetroot are pre-cooled to below 5°C within 24 h after harvest. Forced-air cooling, prompt washing, and hydro-cooling in chlorinated water to under 5°C are essential to maintain carrot freshness. Bunched radish is often hydro-cooled in chlorinated water to an optimum level of 0–4.5°C [51]. Radish can also be pre-cooled using the package icing technique. Generally, room cooling has low or no cost involvement. Forced-air cooling has the risk of root desiccation. Hydro-cooling permits faster cooling but offers the moisture which some

*Phytochemical Changes in Root Vegetables during Postharvest Storage DOI: http://dx.doi.org/10.5772/intechopen.106554*

pathogens require to penetrate the skin of root vegetable [52]. Hence, it is recommended that washed root vegetables should be dried at room temperature before storage. Curing process, which is hardening the skin of potatoes and cassava under temperature and RH conditions that facilitate wound healing, depends on cultivar and on whether they are destined for industry or home consumption.

Surface treatment chemicals that include maleic hydroxide, α–naphthalene acetic acid, methylester, isopropyl N-(3chlorophenyl carbamate) chlorpropham) (CIPC) and 1, 2, 4, 5 tetra chloro-3nitrobenzene are applied on potatoes. These chemicals inhibit meristematic cell division and delay sprout development. Nevertheless, there are safety concerns about the potential toxic and carcinogenic properties of CIPC and its metabolites [53]. Safer alternatives include hydrogen peroxide plus (HPP) [54], 1,4-dimethylnaphthalene (1,4-DMN), essential oils, and ethylene [55]. Gaseous treatments include ozone that has been evaluated for postharvest disease control and other storage uses on potatoes and carrots [56, 57]. However, additional research is needed to define the potential and limits of effective use of ozone for postharvest treatment of whole and minimally-processed vegetables and fruits.

### **4. Storage systems of root vegetables**

Most fresh cassava cultivars deteriorate within 2–3 days after harvest and therefore, processing the roots into storable forms (through sun drying and fermentation) at the farm level is a better option for extending the shelf life and eliminating some toxic compound like cyanide. Some of the commonly used traditional methods include; coating of root with a paste of mud or earth, in-ground storage, field clumps, storage in a box or trench with alternative layers of moist sawdust or wood shavings and cassava roots, and storage in plastic bags [49, 58–60]. Advanced methods that are mainly used on export produce include cold storage/refrigeration at lower temperature range of 0–4°C, freeze drying, and modified atmosphere packaging [20, 49]. Nonetheless, financial and technical constraints have limited the use of advanced methods in many developing countries. Although a number of researches have been conducted on beet, carrot, and radish roots focusing on the potential uses as minimally processed ready-to-use, fresh-cut produce, or as ingredients of processed foods, information on the maintenance of freshness and quality of whole roots during storage is very limited [61]. However, freshly harvested bunched (with tops) and topped beets, carrots, and radish are usually stored between layers of moist sand, leaves, or sawdust in a box in cool place with condition of 0–4°C and 90–95% relative humidity (RH) [62]. The success of Controlled Atmosphere (CA) storage technology requires that the precise levels of CO2 and O2 gases are achieved and maintained within the storage facility. Where CO2 level is too high and O2 level too low, then the root vegetables may be irrevocably damaged [63]. However, there is little or no benefit from controlled atmosphere storage of these vegetable roots.

Potatoes are used for seed, ware, and processing and hence, storage requirements vary depending upon the purpose for which potatoes are to be used. Seed potatoes are required only at the time of planting; therefore, they need to be stored for longer. Generally, seed potatoes are stored at low temperatures (2–4°C). However, most local farmers store seed potato in simple and low-cost diffused light stores (DLS) that use natural indirect light with good ventilation to control excessive sprouting and to produce sprouts which are short, stout, green colored and with higher vigor [64]. Ware and processing potatoes are in demand throughout the year and hence both

short- and long-term storage are needed. Ware and processing potatoes are stored at higher temperatures (8–12°C at 85–90% RH) [65]. Majority of smallholder farmers use traditional storage methods of ware potato. These include piling on the floor or corner in houses, dark stores, DLS, covering potato deep in the soil, stacking tubers in sacks, and heaping potato tubers under the tree shades. Majority of these methods allow keeping potato in good quality for a short period of 2–5 weeks only, depending on the potato variety [66]. Ambient ware potato storage units are also in use and can maintain the marketability of ware potato up to 9 weeks. While advanced ware potato storage methods like evaporative cool storage and cold storage exist, they are not used in most developing countries due to high costs.
