Potato is among the widely grown crop of the world. It is likely that a large portion of the crop is consumed fresh but majority of it is processed into various products, starch being the predominant one. Starch can greatly contribute to the textural properties of many foods and is widely used in food industry as raw material. Since raw potatoes are perishable and accessible only for few months of the year, the food and starch industry has to rely on stored potatoes during off-season. The various varieties of the crop available in the region, storage conditions, pre and post-storage treatments given to the tubers, packaging materials used, etc. are influencing the physical, chemical and functional characteristics of starch extracted from it. The extraction technology from tubers is also having a significant effect on the quality of starch. The knowledge of physical, chemical and functional characteristics of potato starch as affected by varieties, storage treatments and conditions of tubers will help in ensuring uniform and desirable quality of starch for food industry and also provide information for breeding programs and developing the proper postharvest management practices of potatoes.
- extraction methods
- functional properties
- packaging potato starch
- sprout suppressants
- storage conditions
Potatoes are a perishable crop, and due to insufficient, expensive, and widely dispersed refrigerated storage facilities, there are frequent instances of market oversupply, resulting in significant economic damage to farmers and agricultural wastage. Various storage treatments and technologies have been proposed to extend the shelf life of potato tubers. Because raw potatoes are accessible only for few months of the year, the food and starch industry has to rely on stored potatoes during off-season. A proper storage climate helps keep potatoes in excellent condition by avoiding excessive weight loss, microbial spoilage, sprout development, and quality degradation. Potatoes are often stored in long-term postharvest cold storage (8–12°C, 85–90% RH) to retard physiological processes and extend shelf life. Maintaining low temperatures during the storage time is dependent on the tubers’ intended usage
Prolonged storage of potatoes requires sprout inhibition either by use of irradiation or sprout inhibitor chlorpropham (CIPC, isopropyl 3-chlorocarbanilate) treatment [3, 4] or the usage of heat treatment . The CIPC alternatives for sprout inhibition are maleic hydrazide (MH), 1,4-Dimethylnaphthalene, and ethylene . Heat treatment, essential oils of some herbs and spices—also effectively reduce sprouting and can be applied to organically grown potatoes [7, 8]. The sprout inhibiting treatments besides affecting the physiology of tubers also alter the properties of starch .
Starch plays a major role in the sensory characteristics of a wide variety of foods and is extensively used in agro-industrial applications as a thickener, colloidal stabilizer, gelling agent, bulking agent, and water retention agent. Because of the higher granule size and purity of potato starch, as well as the amylose and amylopectin chain lengths and the presence of phosphate ester groups on amylopectin, it stands apart from other cereal starches (corn, wheat, rice, etc.). Potato starch is an excellent texture stabiliser and regulator in food production systems.
The adaptability of starch in a wide range of food items makes it a hot topic among researchers studying carbohydrate polymers. As the genetic basis of the starch changes, so do its physicochemical attributes and functional features, as well as how unique they are in different foods and drinks . Even within the same botanical species, cultivars of the same plant grown in different environments and cultural settings have vastly different starch structures and functions. This diversity results in a wide variety of starches with varying cooking, textural, and rheological characteristics that are linked to their physicochemical, morphological, and thermal properties. The following sections of the chapter deal with the starch characteristics as influenced by extraction methods, cultivars, curing, sprout inhibitors and storage conditions of potato tubers.
2. Effect of extraction methods
Depending on the plant source and intended application for the starch, several techniques can be used to extract it. Different researchers have utilized a variety of extraction methods to separate starch, including steeping periods, extraction temperatures, chemical concentrations and nature, enzymes, and so on. The chemical composition and physical characteristics of starch are both influenced by the extraction processes. To procure a pure product with maximum yield and recovery, lowest cost, and application of a series of interrelated stages allowing the non-starchy fraction to be removed without affecting the granule native structure and minimal incidence on its physico-chemical and mechanical properties, selecting an appropriate starch extraction method is desirable.
The chemical and physical characteristics of starch are altered throughout the extraction process. According to Neeraj
The different extraction techniques resulted in varying proportions of tiny and big starch granules. The Na-bisulphite treatment had the highest percentage of small-sized particles, whereas the other methods had no noticeable variations in particle size. Intact starch granules with smooth surfaces were found in the water-treated starch, but granules of starch treated with Na-bisulphite or propanol-water had somewhat rough and pitted surfaces, as well as fractures inside the granules (Figure 1) . Lin
Phosphorus is present as phosphate monoesters and phospholipids in potato starches . Phosphorus alters the functional characteristics of starches, which is significant both technologically and nutritionally. The phosphate monoesters are covalently linked to the starch’s amylopectin portion. The majority of the phosphate groups are covalently linked to the amylopectin fraction at the C-6 (70%) and C-3 (30%) locations of the glucose units. It has been demonstrated that the phosphate concentration of starches has an effect on their physicochemical qualities and end applications, including starch pasting capabilities, gel strength and clarity, stickiness and viscosity . Neeraj
The variations in WAC between different starches are attributable to the degree to which water binding sites are available in their granules. The hydroxyl groups and inter-glucose oxygen atoms are thought to be the binding sites. The capacity of these starches to interact with water is determined by their ultrastructural (molecular arrangement, amorphous and crystalline regions) and compositional variations (primarily amylose and amylopectin). The capacity of commercial starches to bind water is critical to the quality and texture of some food items because it protects them from effects such as syneresis, which can occur during retorting or freezing . It has been reported that different extraction techniques significantly affected WAC of potato starch. The alkali treatment with NaOH resulted in a greater WAC, but the NaOCl extraction technique resulted in a lower WAC [11, 17]. The increased WAC in alkali treated starch might be due to ions (Na+) diffusing into the amylose-rich amorphous areas of the granules, destroying intermolecular interactions, altering the starch’s crystalline structure, and leading the granules to absorb more water [18, 19]. Fat and protein that are located on the surface of starch granules are crucial for maintaining its structural stability . Additionally, their presence has been demonstrated to significantly slow the rate of starch retrogradation . Lipids have also been observed to form complexes with amylopectin’s outer branches, therefore inhibiting starch retrogradation. It has been reported by Neeraj
Different extraction treatments resulted in significant variations in swelling power and solubility index of the extracted starch. Neeraj
The freeze-thaw stability (syneresis) of starch is a helpful indication of its retrograde tendency. Syneresis is a critical characteristic that is used to determine a starch’s capacity to survive unfavourable physical changes that occur during freezing and thawing. Extraction procedures also have a major influence on syneresis. Neeraj
Granule swelling, granule remnants, leached amylose and amylopectin, as well as the molecular weights and chain lengths of amylose and amylopectin, have all been reported to vary with granule size, resulting in the development of turbidity and reduced light transmittance in refrigerated starch pastes . It has been reported by Neeraj
3. Effect of potato varieties on starch
Tuber starches from different potato breeds vary in terms of crystallinity, granule shape, and other physical and chemical characteristics. The reactivity of the starches in various potato genotypes varied significantly . The accumulation of starch in potatoes is genotype- and environment-dependent, as well as genotype-environment interaction dependent . Due to the variations in tuber development rates amongst cultivars, the harvest dates and hence the dry mater accumulation varied for different potato cultivars. Early maturing cultivars showed lower dry matter content and a lower starch content than late maturing types. Kufri Chipsona-4 produced the most, followed by Kufri Badshah, Kufri Sindhuri, and Kufri Bahar; and Kufri Pushkar produced the least amount of starch. Since Kufri Chipsona-4 is a medium to late maturing variety, it produced more starch than other cultivars .
Singh and Singh  reported that Kufri Badshah (KB) and Kufri Jyoti (KJ) starch paste showed higher light transmittance and lower turbidity values than Kufri Pukhraj (KP) potato starch pastes. Kaur
The water absorption capacity (WAC) has been reported to be different for the starches extracted from different varieties. Singh and Kaur  reported that Kufri Chandermukhi small granule fraction showed the highest WAC as compared to Kufri Sindhuri and Kufri Jyoti. Kaur
The phosphorous content of extracted starch was found to be different for different potato varieties. It was minimum in Kufri Pushkar followed by Kufri Sindhuri, while it was maximum in Kufri Chipsona-4 [11, 17]. Pineda-Gomez
There were marked differences in
Starches’ swelling ability and solubility are strongly linked. Neeraj
Syneresis, or freeze-thaw stability, is a critical characteristic used to assess a starch’s capacity to survive the undesired physical changes that occur during freezing and thawing. Syneresis was discovered to be least in starch extracted from Kufri Pushkar, followed by Kufri Bahar, and to be most in Kufri Chipsona-4 [11, 17].
4. Effect of curing treatment of tubers
Freshly harvested potatoes have very short shelf life due to thin skin. Curing is accomplished by holding potatoes in dark at ~22°C and RH 90% for 10—15 days. During curing potatoes utilize the reserved food material to provide energy and metabolites to heal bruises and cracks and to develop periderm layer making the peel thick and impermeable to water. The various changes taking place in the characteristics of extracted starch from different varieties of potato due to curing of tubers was studied in detail by Neeraj
Curing did not significantly affect the size of the starch particles and syneresis . The syneresis exhibited a significant positive correlation with amylose content. Though the amylose content was slightly reduced by curing, still the syneresis was not affected [11, 17]. This might be because the amount of the change in amylose concentration was too little to have a meaningful influence on syneresis, or because other variables such as crude fibre, fat, protein, and granular structure also playing a role in syneresis .
5. Effect of sprout inhibiting treatments
The sprout inhibiting treatments besides affecting the physiology of tubers also alter the properties of various biochemical constituents. CIPC, also referred as chlorpropham is the most commonly used sprout suppressant on potatoes when stored at 8–12°C. Potatoes can also be stored for at least 12 weeks at either 8 or 18°C without sprouting, if tubers are dipped in hot water (57.5°C and 20 or 30 min) [5, 40]. It was reported by Hu
Potatoes treated with CIPC to inhibit sprouting contained greater amounts of total starch as well as resistant starch (RS) than untreated potatoes tubers . Lu
Neeraj  studied the effect of various sprout inhibiting treatments viz., hot water dip treatment (HWT, 57.5 ± 0.1°C for 20 min) and single spray of 50% formulation of CIPC treatments on the characteristics of starch extracted from Kufri Chipsona 4 variety of potato stored at low temperature (12 ± 1°C). It was observed that significantly higher starch yield was observed in CIPC treated tubers followed by hot water treatment and untreated. The CIPC treated tubers retained higher starch than other treatments until the end of the storage period, which can be attributed to inhibited sprouting and low respiration rates. Hot water treatment may also have resulted in higher starch yield because of its inhibitory role on sprouting of tubers. Kyriacou
There was no significant effect of HWT on particle size, however, CIPC treatment significantly increased the percentage of small size particles of starch from LT stored tubers . Ezekiel
The effects of CIPC and HWT were found to be non-significant with respect to untreated tubers for extracted starch’s moisture content, protein content, fat content, crude fiber, ash content, purity, WAC and colour whiteness values; while starch yield, amylopectin, phosphorus content, swelling power, solubility, light transmittance and peak viscosity were higher for starch extracted from tubers treated with CIPC than HWT . The nonsignificant effect on purity of starch was attributed to nonsignificant changes in moisture, fat, crude fibre, protein and ash contents of the starch extracted from tubers subjected to various sprout inhibiting treatments.
Hot water dip treated tubers resulted in significantly lower swelling power than untreated tubers at RT storage, however, significantly higher swelling power was observed in CIPC treated tubers stored at LT . Additionally, Lu
Significantly lower syneresis was observed in the starch extracted from CIPC treated tubers followed by HWT tubers and untreated tubers . Singh
6. Effect of storage conditions and packaging
The starch content of potatoes has been reported to decrease during storage due to conversion of starch to sugar and its utilization in respiration . The rate of starch depletion and sugar buildup vary with cultivar and storage temperature, presumably due to variations in enzyme activities . Johnston
Neeraj  reported that as the storage time for tubers increased, the moisture, fat, ash, crude fibre, amylopectin, phosphorus, water absorption capacity, light transmittance, and peak viscosity of the extracted starch increased; while yield, purity, amylose, swelling power, solubility, syneresis, and colour whiteness value decreasedIt has been reported that pastes prepared from potato starches with higher percentages of small granules exhibit lower syneresis. The decrease in syneresis of starch extracted from stored tubers could be due to the decreased amylose, and increased amylopectin, phosphorus and percentage of small size particles [17, 18].
Neeraj  reported that the starch extracted from the tubers stored at low temperature (LT) with different packaging viz., nylon mesh bags or MAP or vacuum did not show significant differences in its moisture, fat, protein, ash, crude fiber, purity, amylose, amylopectin, WAC, swelling power and whiteness values; while minimum syneresis and maximum starch yield, phosphorus content, solubility, light transmittance and peak viscosity were observed for starch extracted from tubers packed in net bags followed by vacuum and modified atmosphere packaging. Significantly higher peak viscosity of starch was observed for starch extracted from net bag packed tubers followed by vacuum, while it was minimum in modified atmospheric packaging. The various packaging methods did not significantly affect the starch yield from tubers stored at room temperature, however, for tubers stored at low temperature, maximum starch yield was observed for tubers packed in net bags, while modified and vacuum packed tubers were showing at par but lower starch yields. Similarly, it was reported by Mare and Modi  that Taro cormels of Dumbe-dumbe and Pitshi packaged in mesh bags also displayed higher starch content compared with those packaged in polyethylene bags and boxes.
The growing starch markets have led to food industries to a constant demand for starches with specific properties that meet the demands of applicability. The quality of extracted starch form potato tubers, however, are significantly affected by environmental, cultural and storage conditions. The available information of the various physico-chemical and functional characteristics of potato starch as affected by extraction methods, varieties, curing, sprout inhibitors, and storage conditions. Some more information still need to be generated with respect to the effect of preharvest cultural practices, organic raising, extent of sprouting of tubers, application of other sprout suppressants (irradiation, isopropyl phenylcarbamate, ozone, ethylene, MH, carvones, etc) and various storage structures on the quality of extracted potato starch. The information w.r.t. verities may be helpful in identifying phenotyping trait(s) in potato breeding processes to create special potato genotypes for manufacturing of starch with the characteristics specially tuned for certain industrial processing technologies. On the basis of information, the potato starch industry may also select specifically pre- and postharvest treated stored potatoes of a given variety for extracting starches having the desired functional characteristic.
Acronyms and abbreviations
amylose amylopectin isopropyl N-(3-chlorophenyl) carbamate hot water treatment low temperature resistant starch X-ray diffraction swelling power gelatinization endset temperature gelatinization onset temperature gelatinization peak temperature temperature at which viscosity development is initiated water absorption capacity peak height indices enthalpies of gelatinization.
isopropyl N-(3-chlorophenyl) carbamate
hot water treatment
gelatinization endset temperature
gelatinization onset temperature
gelatinization peak temperature
temperature at which viscosity development is initiated
water absorption capacity
peak height indices
enthalpies of gelatinization.