Impact of processing on potato phytochemicals
Potatoes (Solanum tuberosum) are an important staple crop in both developed and developing countries around the world. These tubers offer an important source of nutrients, micronutrients, and health-promoting phytochemicals to the diet. However, reported content and process stability of phytochemicals in commercial potatoes and potato products is inconsistent. The objectives of this research were to compare phytochemical content in white/yellow and pigmented commercially relevant varieties, determine changes in phytochemical content of select potato varieties through commercial processing, and assess differences in phytochemical content between freshly “home” prepared and reconstituted, commercially processed white and sweet potato products. To carry out the first objective, phenolic acids, anthocyanins, and carotenoids were analyzed in whole and flesh of nine commercial potato varieties. Total chlorogenic acids (CQAs), the primary phenolic acid in potatoes, ranged from 43-953 mg/100 g dw and were found in greater concentrations in the whole of all varieties compared to flesh, suggesting concentration in the peel. Higher levels of CQAs were also observed in pigmented potatoes compared to white/yellow-fleshed potatoes (318-953 and 43-88 mg/100 g dried whole potato, respectively). 5-O-Caffeoylquinic acid (5-CQA) was the primary chlorogenic acid isomer detected in all varieties of potato, followed by 4- O- and 3-O-caffeoylquinic acid (4-CQA and 3-CQA). Acylated anthocyanins in red potatoes were primarily cyanidin and pelargonidin derivatives, while those in purple varieties were primarily derivatives of petunidin with smaller amounts malvidin and delphinidin. For the second objective, four varieties (2 purple, 1 red, 1 white) of processed, dried, and ground commercial products were obtained from McCain foods, including raw flesh without skin (FNS), blanched+frozen (BF), +microwaved (BFM), and blanched+par-fried+frozen (BFF), +baked (BFFO) or +fried (BFFF). Retention of phenolics ranged from 49-85% for pigmented varieties and 32-55% for white. For purple and red varieties, CQA levels were significantly lower (p<0.05) in BFF, BFFO, and BFFF compared to FNS, BF, or BFM products. For white, CQA levels were lower (P<0.05) in all processed products compared to FNS, but no differences were observed between processing levels. Retention of anthocyanins through all forms of processing was found to be high (69-129%). For the last objective, CQA and beta-carotene were compared in freshly prepared versus commercially produced and reconstituted classic fries, fresh-style fries, hash browns, sweet potato fries, and sweet potato wedges. Levels of CQA did not differ for classic fries, fresh-style fries, or sweet potato fries, but were significantly (p<0.05) lower in industrial baked and fried sweet potato wedges and baked and pan-fried hash browns. Sweet potato β-carotene was higher in commercial baked wedges (30 mg/100g dw) compared to fresh prepared (26 mg/100g) (p<0.05), but no other differences between fresh and commercial products were found. These results suggest that commercial blanching, freezing, and microwaving have an overall mild impact on phytochemical levels in raw potatoes compared to par-frying and subsequent baking or frying. Additionally, industrial products compare favorably to freshly prepared products in recovery of phytochemicals suggesting that both commercially prepared and freshly prepared products would provide similar delivery of health promoting phytochemicals.
Ferruzzi, Purdue University.
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