Domestic cooking methods affect the phytochemical composition and antioxidant activity of purple-fleshed potatoes
Introduction
Phytochemicals are bioactive non-nutrient plant compounds found in fruits, vegetables, grains and other plant foods and are broadly classified as carotenoids, phenolics, alkaloids, nitrogen-containing compounds, or organosulfur compounds (Nebeling, 2003). Numerous studies have demonstrated a negative correlation between the intake of phytochemicals and various diseases (e.g., chronic inflammation, cardiovascular diseases, cancer and diabetes) (Williams et al., 2013). As the dominant tuber crops worldwide (King & Slavin, 2013), potatoes contain numerous phytochemicals that are considered important due to their beneficial effects on health and therefore highly desirable in the human diet (Wolfe et al., 2008). Phytochemical extracts from potatoes have been reported to protect against acute liver injury and oxidative damage to erythrocytes (Singh & Rajini, 2008), reduce breast cancer in rats (Thompson et al., 2009), exhibit anti-inflammatory effects and even benefit heart and eye health (Ezekiel, Singh, Sharma, & Kaur, 2013).
Potatoes are usually cooked in different ways prior to consumption according to the recipes and culinary traditions of the various countries. For example, steaming, boiling and frying conform to the dietary habits of Western society, whereas stir-frying is used to prepare most homemade dishes in China (Ruiz-Rodriguez, Marín, Ocaña, & Soler-Rivas, 2008). Those cooking conditions are distinct (e.g. high temperature and excess oil involved in frying, limited oil, long cooking time and high temperature in air-frying, short cooking time and small size of strips in stir-frying) and induce a series of changes in the physical characteristics, chemical composition and enzyme modifications of foods (Rothwell et al., 2015). Most recent studies focused on the phytochemical and antioxidant activity undergone by potatoes during domestic cooking, but the conclusions were inconsistent and sometimes contradictory. For example, Blessington and coworkers (2010) reported that boiling, baking, frying and microwaving, significantly increased the total phenolic content, chlorogenic acid content and antioxidant activity in potatoes, whereas Xu, Li, Lu, Beta, and Hydamaka (2009) concluded that all cooking methods (boiling, baking and microwaving) induced decreases in phytochemical concentrations and antioxidant activity. Faller and Fialho (2009) showed that despite a significant increase in the total phenolic content, the antioxidant activity of potatoes decreased significantly, whereas Burgos et al. (2013) reported that boiling increased the total phenolic content and antioxidant activity and significantly decreased the total anthocyanin content. This difference may be attributed to the different species of potato examined in the studies, the pretreatment and cooking conditions applied, and the different analytical methods used. Thus, a systematic study of the effects of different cooking methods on phytochemical changes is needed.
Potatoes are food crops grown worldwide that are considered a good source of phytochemicals with interesting and health-promoting properties. With the increasing demand for novel functionality and health awareness, one variety of potato with purple-colored flesh containing high levels of anthocyanins has attracted much attention from researchers and the public (Ezekiel et al., 2013). However, the available information of the effects of cooking methods on selected phytochemicals and the antioxidant activity of purple-fleshed potatoes is insufficient. Purple potatoes contain an abundance of phytochemicals and should thus be a suitable model for evaluating the effects of domestic cooking methods on the phytochemical composition in potato.
Thus, in the present study, we conducted a systemic evaluation of the effects of different domestic cooking methods, including boiling, steaming, baking, microwaving, frying, on the phytochemical composition (i.e., total phenolics, phenolic acids, anthocyanins, carotenoids) and antioxidant activity, and the correlations between changes in these phytochemicals and antioxidant activity were also established. In particular, the effects of two other cooking methods (stir-frying, which is used to prepare most homemade dishes in China, and air-frying, a new technique for producing healthy fried potato strips) were evaluated for the first time in the present study.
Section snippets
Plant materials and cooking methods
Purple-fleshed potatoes (Heimeiren) (length 6–8 cm, diameter 3–4 cm, weight 100–120 g) and soybean oil were obtained from a local supermarket (Hangzhou, China). For boiling, steaming, baking and microwaving, whole tubers (unpeeled) were cooked, and a stainless-steel probe was inserted in the tubers to evaluate the cooking time (Table 1). For normal frying and air-frying, potatoes (unpeeled) were washed and cut into strips (8 × 7 × 60 mm) manually, whereas for stir-frying, the strips measured 2 × 3 × 60 mm.
Effect of cooking treatments on proximate composition
Table 2 shows the proximate composition of the samples after being subjected to different cooking conditions. The results show that frying, air-frying and stir-frying, significantly increased both the protein and crude fat contents (41.00%, 21.39% and 27.99% increases in protein and increases of 4.07 ± 0.15, 7.60 ± 0.37, and 3.49 ± 0.42 g/100 g DW in fat, respectively) (DW: dry weight). However, the other cooking methods, i.e., boiling, steaming and microwaving, induced no significant differences in
Conclusion
The present study clearly demonstrates that the antioxidant activity and the phytochemical composition of potatoes were affected by different cooking methods. Among the different cooking methods tested, steaming and microwaving were observed to retain the greatest amounts of phytochemicals and antioxidant activity, making these methods preferable for cooking potatoes from a health-promotion point of view (Palermo et al., 2014). However, the frying methods caused severe losses of vitamin C and
Conflict of interest
The authors declare that they have no conflicts of interest.
Acknowledgments
This work was supported by National Science-Technology Support Plan Projects (2014BAD04B01) and the Center for Basic Funds for Universities (2-2050205-15-001).
References (35)
Total and individual carotenoid profiles in Solanum phureja of cultivated potatoes: I. Concentrations and relationships as determined by spectrophotometry and HPLC
Journal of Food Composition and Analysis
(2009)- et al.
Total phenolic, total anthocyanin and phenolic acid concentrations and antioxidant activity of purple-fleshed potatoes as affected by boiling
Journal of Food Composition and Analysis
(2013) - et al.
Anthocyanins from pigmented potato (Solanum tuberosum L.) varieties
Food Research International
(2005) - et al.
Beneficial phytochemicals in potato – a review
Food Chemistry
(2013) - et al.
The antioxidant capacity and polyphenol content of organic and conventional retail vegetables after domestic cooking
Food Research International
(2009) - et al.
Review of the effects of food processing and formulation on flavonol and anthocyanin behaviour
Journal of Food Engineering
(2012) - et al.
The effect of frying on anthocyanin stability and antioxidant activity of crisps from red- and purple-fleshed potatoes (Solanum tuberosum L.)
Journal of Food Composition and Analysis
(2013) - et al.
Impact of selected factors-cultivar, storage, cooking and baking on the content of anthocyanins in coloured-flesh potatoes
Food Chemistry
(2012) - et al.
Influence of cooking on the levels of bioactive compounds in purple majesty potato observed via chemical and spectroscopic means
Food Chemistry
(2015) - et al.
Nutritional composition of freshly harvested and stored Latvian potato (Solanum tuberosum L.) varieties depending on traditional cooking methods
Journal of Food Composition and Analysis
(2011)
Influence of processing on the antioxidant properties of fruit and vegetables
Trends in Food Science & Technology
Effect of thermal processing on anthocyanin stability in foods; mechanisms and kinetics of degradation
Trends in Food Science & Technology
Effects of cooking methods on polyphenols, pigments and antioxidant activity in potato tubers
LWT-Food Science and Technology
Content of polyphenols in coloured and yellow fleshed potatoes during dices processing
Food Chemistry
DPPH antioxidant assay revisited
Food Chemistry
Antioxidant-mediated protective effect of potato peel extract in erythrocytes against oxidative damage
Chemico-Biological Interaction
Bioactivity and protective effects of natural carotenoids
Biochimica et Biophysica Acta (BBA) – Molecular Basis of Disease
Cited by (147)
How to cook sweet basil (Ocimum basilicum L.) leaves to obtain the highest nutrient bioaccessibility and bioactive compounds?
2024, International Journal of Gastronomy and Food ScienceDietary purple potato supplement attenuates DSS-induced colitis in mice: impact on mitochondrial function
2024, Journal of Nutritional BiochemistryEffect of thermal processing on bioactive compounds contents and antioxidant capacities of unripe and ripe Solanum anguivi Lam. fruit accessions
2024, Journal of Applied Research on Medicinal and Aromatic PlantsSoursop fruit supply chains: Critical stages impacting fruit quality
2023, Journal of Agriculture and Food Research