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Effects of boiling, steaming, microwaving, roasting and frying on proximate composition, carotenoids and antioxidant activities of orange-fleshed sweet potato (OFSP) were investigated. Retentions of 66.30–82.19% of β-carotene contents were observed after boiling (15–35 min), steaming (15, 35 and 45 min) and microwaving (15 min). High retentions of (9Z)-β-carotene were noted after all cooking processes, being 515.40% after steaming at 45 min. α-carotene was highly retained after boiling at 15–35 min (103.77–106.74%). A high retention of 91.37% in total polyphenol contents was noted after steaming (35 min), whereas 98.98–102.36% of vitamin C was retained after steaming (15–45 min) and microwaving (15 min). All cooking processes improved antioxidant activities of OFSP, and the correlation analysis between carotenoid contents and antioxidant activity suggested that antioxidant activity could be attributed to the higher contents of (9Z)-β-carotene. It was suggested that boiling and steaming are preferable to maintain carotenoids and antioxidant activities of OFSP.

Sweet potato leaf polyphenols (SPLPs) have shown potential health benefits in the food and pharmaceutical industries. Nowadays, consumption of SPLPs from animal feeds to foodstuff is becoming a trend worldwide. However, the application of SPLPs is limited by their low bioavailability and stability. β-lactoglobulin (βlg), a highly regarded whey protein, can interact with SPLPs at the molecular level to form reversible or irreversible nanocomplexes (NCs). Consequently, the functional properties and final quality of SPLPs are directly modified. In this review, the composition and structure of SPLPs and βlg, as well as methods of molecular complexation and mechanisms of formation of SPLPsβlgNCs, are revisited. The modified functionalities of SPLPsβlgNCs, especially protein conformational structures, antioxidant activity, solubility, thermal stability, emulsifying, and gelling properties including allergenic potential, digestibility, and practical applications are discussed for SPLPs future development.

Milk proteins and polyphenols are increasingly being studied as functional ingredients due to the epidemiologically-proved health benefits. In this study, composite β-lactoglobulin (β-lg) or β-lactoglobulin nanoparticles (β-lgNPs)-3,5-di-O-caffeoylquinic acid (3,5diCQA) with superior physicochemical and antioxidant activity (AA) were produced using β-lg and 3,5-di-O-caffeoylquinic acid. The main interactions between β-lg or β-lgNPs with 3,5diCQA were hydrogen bonding and hydrophobic effects. The 3,5diCQA caused a decrease in α-helix and β-sheet structure with a corresponding increase in unordered structure. Compared to β-lg alone, composite β-lg or β-lgNPs-3,5diCQA slightly decreased the particle size but increased their negative surface potentials especially for β-lg or β-lgNPs at a molar ratio of 5:1. The addition of 3,5diCQA appreciably improved the AA in a dose-dependent manner. These results shed light on the structural, physicochemical, and AA of composite β-lg or β-lgNPs-3,5diCQA non-covalent complexes, important for application as functional ingredients in food solutions as well as in the pharmaceutical industry.

This chapter introduces the main categories, individual phenolic composition, physiological functions, processing stability, and utilization of polyphenols from sweet potato roots and tops. It starts by presenting the definition and chemical composition of anthocyanins and caffeoylquinic acids (CQAs) from sweet potato roots and tops. Then the physiological functions of polyphenols from sweet potato, including antioxidant activity, antimutagenic effect, and anticancer activity, are introduced, followed by a detailed introduction into the effect of different cooking and processing conditions, including different pH values, heating temperature, and light treatment on the stability of anthocyanins and CQA s from sweet potato roots and tops. At the end of this chapter, the research and development trend of sweet potato polyphenols are presented.

This chapter introduces the extraction, purification, antioxidant activity, and individual phenolic compound composition of sweet potato leaf polyphenols. It starts by introducing sweet potato leaves and polyphenols in sweet potato leaves. It then focuses on the extraction and purification of polyphenols from sweet potato leaves, especially the purification process of polyphenols from sweet potato leaves by AB-8 macroporous adsorption resin. By the end of the chapter, the individual phenolic compound composition and antioxidant activity of the purified sweet potato leaf polyphenols are introduced, which suggest that purification by AB-8 macroporous resin was highly efficient, economic, and environmentally friendly, and has a great industrial production potential.

The quest to determine and use polyphenolic compounds present in fruits and vegetables as natural antioxidants has recently attracted much attention due to their beneficial health effects. In this study, the total polyphenol content (TPC), total flavonoid content (TFC), total anthocyanin content (TAC), antioxidant activity (AA), and individual polyphenol components of Simon No. 1, Yuzi No. 7, Shangshu 19, and Pushu 32 sweet potato cultivars (edible parts: leaf, stalk, stem, skin, and flesh) were investigated. TPC, TFC, and TAC values ranged from 440 ± 0.17-12080 ± 0.58 CAE mg/100 g DW, 94 ± 0.08-4210 ± 0.74 QE mg/100 g DW, and 7 ± 0.01-1010 ± 0.54 CGE mg/100 g DW, respectively. Yuzi No. 7 sweet potato cultivar contained significantly higher amounts of TPC, TFC, TAC, and AA in all its edible parts, followed by Pushu 32, Simon No. 1, and Shangshu 19 in that order. Regardless of the sweet potato cultivar used, TPC, TFC, and TAC of sweet potato leaves were significantly higher than those of other edible parts. High-performance liquid chromatography revealed 19 individual phenolic compounds. In general, 3,5-di- O-caffeoylquinic acid, astragalin, and cyanidin were the predominant phenolic acid, flavonoid, and anthocyanin compounds, respectively. The correlation analysis suggested that higher AA could be attributed to higher polyphenol content. Based on our results, edible parts of Yuzi No. 7 sweet potato cultivar presented the highest amounts of polyphenol content and AA suggesting the possibility of utilizing this cultivar by farmers and the food industry as a functional food product.