**Table 2.**

 *Summary of studies on effects of storage system on the quality of selected root vegetables.* sugar content is linked to the development of harsh, and oily flavor in carrots during prolonged storage [96].

Significant differences have been observed in the content of main beetroot betcyanins (betanin and isobetanin) during cold storage of red beetroot at 5°C for 196 days [71]. The content of betanin in red beetroot peel decreased in the first 140 days of cold storage and then slightly increased (**Table 2**). In terms of isobetanin, until 98 days, an increasing trend and afterward, up to 140 days of storage, a light decrease were noticed [71]. In [72] it was shown that after 1 month of cold storage, there was an increase in beetroot water loss that resulted into increased total dry matter content. The total phenolic content of beetroot in cold storage increased after 4 months of storage. In another study, the nitrate content in beetroot increased significantly after 1 month of cold storage [73], and no further significant increase was observed after a cold storage period of 4 months. In [61], there was no significant change in total sugar content of 11 beetroot genotypes stored under optimal cold storage conditions at 1 ± 1°C and 90–95% RH for 7 months. Additionally, beetroots retained their levels of total soluble sugar contents after 1 month of cold storage, and the levels decreased after 4 months of cold storage. Therefore, it is beneficial to use these beetroot genotypes freshly or within the first month of storage, when a high sugar content is desired.

Freshly harvested cassava roots transpire and loose moisture, which reduces their quality during storage. Cassava undergoes postharvest physiological deterioration (PPD) once the roots are separated from the main plant. As a result of this mechanical damage (wounding), the roots respond with a healing mechanism that initiates about 15 min after damage, and fails to switch off in harvested roots [97]. This is observed as a blue/black or brown discoloration of the vascular parenchyma (vascular streaking) within 24–72 h of harvest [20] rendering it unpalatable. As described by Beeching [98, 99], this mechanism involves an oxidative burst of the superoxide radical (O2−), which is followed by the further production of reactive oxygen species, altered gene expression, and the accumulation of secondary metabolites. This physical and biochemical change is often followed by microbial deterioration and root tissue softening.

Traditional methods have been shown to extend cassava shelf life for few days during which, the cyanide, moisture, and starch content in the root decreases while the ash, sugar, crude fiber as well as the acidic content increases with the length of storage [49, 58, 59]. Generally, temperatures of about 20–30°C and low RH between 65 and 80% encourage deterioration [100]. Therefore, storage of cassava under high relative humidity and limited oxygen conditions, for example, in polyethylene bags, storage boxes, and coating with paraffin wax, can reduce water loss and oxidative stress [101]. Besides, Rickard [102] reported that at 80–90% RH, cassava roots showed a typical wound-healing response with periderm formation occurring in 7–9 days at 35°C and 10–14 days at 25°C.

Prolonged in-ground storage has been shown to increase the size of the root. However, the roots become more woody and fibrous, and with decreased palatability and amount of extractable starch, besides becoming more susceptible to attack by pathogenic microorganisms (**Table 2**) [49, 58]. Covering cassava roots with paraffin wax by dipping the root in paraffin wax (at a temperature of 55–65°C for a few seconds) after treatment with fungicide has been reported to prolong shelf-life of cassava roots up to 2 months (**Table 1**) [49, 68].

Cassava roots can also be stored for 2 weeks between 0 and 4°C without any internal deterioration, and after 6.5 months of storage, the part of the root without decay usually is in excellent condition for human consumption [49]. At temperatures

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

above 4°C, roots develop the PPD symptoms more rapidly and have to be discarded after 2 weeks of storage [49]. A study on the effect of the total carotenoids content in cassava root on the reduction and delay of postharvest deterioration showed that cassava roots kept at 10°C and 80% RH can remain fresh till after 2 weeks [100]. Thus, higher carotenoid can reduce or delay the onsets of PPD and extend the shelf life of the root. Wijesinghe and Sarananda [103] reported that freezing of fresh cassava for up to 8 weeks resulted into loss in water and increase in dry matter, that was driven by the high vapor pressure deficit created between the product and the low RH in the refrigerator environment. Consequently, the water stress which remained of acceptable eating quality although none remained as good as the freshly harvested ones.

Physicochemical parameters that determine quality of radish are well maintained in lower storage temperature of 0°C hence it is recommended for extended storage period of radish. Studies by Chandra et al. [90] showed that weight losses of radish roots were remarkably lower (<3%) in radish packed with micro perforated HDPE film in plastic crate and that cured then packed in micro perforated HDPE film in PC while the cured sample maintained its total soluble solids, and flesh and skin firmness. Both samples also recorded lower scores of black spot, surface shrinkage, and fungal infection incidence (**Table 2**). About 1.3% weight loss of unpacked topped radish root was noted after 9 days of storage at either 5°C or 10°C [104]. However, severe weight loss of radishes (about 52%) was noted just after 3 days of storage when radishes were stored at room temperature (20 ± 2°C) without leaves [91]. In a related study, a weight loss of about 2.5% was noted when whole radishes were stored at 1°C or 5°C for 10 days, whereas this loss reached nearly double when they were stored at 10°C [92]. These results indicate that storage temperature greatly affects the fresh weight retention ability of radish. In another study, the concentration of isothiocyanate sulforaphene and myrosinase activity were measured in two radish cultivars, namely "Chungwoon plus" (CP) and "Taebaek" (TB), during storage at 0°C for 4 months. After the storage period, the sulforaphene concentrations in the CP and TB radish cultivars decreased by 81% and 40%, respectively [89]. Also, the myrosinase activity decreased in both cultivars which subsequently decreased the formation of sulforaphene [89]. Glucosinolates, lipid-soluble vitamins E and K contents, and primary metabolites were measured from topped radish root stored at 1°C for 90 days. The results indicated that the tested storage conditions had no effect on the concentration of aliphatic glucosinolates present in radish [88].

Use of low temperatures (i.e., 2–4°C) and potato sprout inhibitors are the widely used storage treatments on freshly harvested potatoes. Curing potatoes allows the formation of a protective layer (wound periderm) over areas of potato that could have been damaged during harvesting. Curing has been reported to limit weight loss and to prevent the penetration of pathogenic microorganisms. In a study in which the effects of various curing and storage conditions (i.e., duration, temperature, and RH) on the quality of two potato cultivars, "Moonlight" and "Nadine" were investigated, high curing RH (93%) led to significantly lower skin browning, shriveling, and weight loss in both cultivars, and significantly lower incidence of rot in "Nadine" than low curing RH (62%) [105]. A 7 days curing at >90% RH and at least 15°C was recommended.

Sprout inhibitors (e.g., ethylene) and treatments to inhibit microbial establishment on harvested potatoes are reported to be effective but with varied secondary effects on potatoes. Previous studies have reported that ethylene application can either shorten or delay potato dormancy period depending on both treatment duration and concentration [106]. Furthermore, a continuous application of ethylene [69] and/or early application (applied after appearance of first sprouting) [70] is reported

to prevent potato sprouting. However, this can also increase the content of reducing sugars (primarily glucose and fructose) in potato, thus limiting its use for processing potatoes. High levels of reducing sugars in processing potatoes causes cold induced sweetness [107] that is responsible for the dark brown color on processed potato products that gives a bitter taste [108]. In a separate study, a single treatment with HPP or CIPC resulted, after 6 months of storage at 10 ± 1°C, in sprouting rates of 61% and 58%, respectively, vs. 87% in the untreated control [54]. From preliminary experiments in [48], potatoes exposed to UV-C light at five different intensities (0.0, 3.4, 7.1, 10.5, and 13.6 kJ m−2) and stored in the dark at 20°C and 80% RH for 40 days showed reduction in sprout length and development up to 20 d. However, this effect diminished during storage. Also in [47], potatoes exposed to gamma Irradiation (0, 50, 100, and 150 Gy levels) on different dates (10, 30, and 50 days after harvest) were studied during prolonged storage at 8 and 16°C. Results indicated that indicated that early and higher irradiation levels significantly decreased sprouting, percent weight loss and specific gravity of potato. However, the loss of ascorbic acid, and reducing and non-reducing sugars significantly increased by delay in irradiation whereas the sugars and ascorbic acid content was decreased by irradiation. Higher storage temperature (16°C) caused greater loss of ascorbic acid. A delay in irradiation and storage at high temperature was not recommended [47]. A study in [83] showed that potatoes buried at deeper depths (overground/pit storage) accumulated a lot of respiratory heat. This heat has been reported to promote potato sprouts [84]. Sprouting results in remobilization of storage compounds mainly starch and proteins as sprout tissue is built from the potato reserves. This increases the rate of respiration as well as evaporation [109], and consequently weight loss. Also, vitamin C is adversely affected by sprouting [47]. Sprouting and sprout growth contributes to formation of toxic glycoalkaloids (TGA). This involves the buildup of chlorophyll beneath the peel, a process known as "greening" [110]. Greening in potatoes is associated with the TGA solanine accumulation. In a study where six potato cultivars were analyzed for TGA content after 6 and 14 weeks of storage at either 10 or 4°C, results indicated that the exposure of some cultivars, to low temperatures within 2 weeks of harvest resulted in a relatively rapid accumulation of TGA to levels close to or exceeding the recommended safe maximum level of 200 mg of TGA per kilogram of fresh weight [86].

Nevertheless, storage of potatoes at low temperatures has been shown to significantly decreases the content of vitamin C [87, 111, 112], although in [82] it was noted that even with the decrease in vitamin C, a significant amount was still retained. The decrease in vitamin C content is attributed to its use, in the potato, as an antioxidant compound in response to oxidative stress caused by low temperature storage. In [87], an evaluation for antioxidant parameters of potatoes stored at room temperature, 15°C and 4°C for 90 days showed that all phenolic acid content increased with storage time, except para-coumaric acid which decreased at 4°C. Similarly, a separate study showed an increase in chlorogenic acid, caffeic acid, and sinapic acid content during storage of potatoes for 90 days at 3°C [81].

High temperatures can also influence respiration rate, development of decay causing organisms, greening, and shrinkage in stored potatoes [113]. A study on the effect of three store types (ambient charcoal-cooled, traditional grass thatched hut and diffused light store [DLS]) on the quality of potatoes stored for 56 days at temperatures 9.7–19.4°C and RH 65–93%, results showed increased weight loss, greening ,and shrinkage in potatoes stored in DLS (temperature 16.15–19.35°C; RH 65–89%) [85]. Additionally, there was a significant increase in the reducing sugar content. The starch content in potato samples from the three stores decreased with increasing storage time.
