Effect of Different Drying Techniques on the Resistant Starch, Bioactive Components, Physicochemical and Pasting Properties of Cardaba Banana Flour

The multifactorial phenomenon of enzymatic hydrolysis resistance in unripe banana flour and its starch: A concise review

Unripe banana flour starch possesses a high degree of resistance to enzymatic hydrolysis, a unique and desirable property that could be exploited in the development of functional food products to regulate blood sugar levels and promote digestive health. However, due to a multifactorial phenomenon in the banana flour matrix-from the molecular to the micro level-there is no consensus regarding the complex mechanisms behind the slow enzymatic hydrolysis of unripe banana flour starch. This work therefore explores factors that influence the enzymatic hydrolysis resistance of raw and modified banana flour and its starch including the proportion and distribution of the amorphous and crystalline phases of the starch granules; granule morphology; amylose-amylopectin ratio; as well as the presence of nonstarch components such as proteins, lipids, and phenolic compounds. Our findings revealed that the relative contributions of these factors to banana starch hydrolytic resistance are apparently dependent on the native or processed state of the starch as well as the cultivar type. The interrelatability of these factors in ensuring amylolytic resistance of unripe banana flour starch was further highlighted as another reason for the multifactorial phenomenon. Knowledge of these factors and their contributions to enzymatic hydrolysis resistance individually and interconnectedly will provide insights into enhanced ways of extraction, processing, and utilization of unripe banana flour and its starch.

Quality attributes of the developed banana flour: Effects of drying methods

The study aims to investigate the effects of different drying methods on the changes in functional properties, physicochemical composition, bioactive compounds, antioxidant activity, sensory attributes, and microstructural quality of the banana flours. Two local banana cultivars, Mehersagar and Sabri, were dried to produce flour using four distinct drying methods: freeze drying (FD), cabinet drying (CD), microwave oven drying (MOD), and forced air oven drying (FOD). The functional properties of the developed banana flours were observed where the findings were as water holding capacity (0.93 ± 0.06-2.74 ± 0.04 g water/g dry sample), oil absorption capacity (0.87 ± 0.06-2.22 ± 0.10 g oil/g dry sample), swelling capacity (4.62 ± 0.02-5.05 ± 0.03 g paste/g dry sample), bulk density (0.54 ± 0.04-0.81 ± 0.02 g/ml), tapped density (0.62 ± 0.04-0.93 ± 0.03 g/ml) and Carr's Index (9.38 ± 0.47-13.58 ± 0.43%). Freeze-dried Mehersagar cultivar's flour showed the leading functional properties with good flowability and cohesiveness. The physicochemical parameters of the flours also revealed significant differences (p < 0.05) in lightness (L*) (50.51 ± 1.49-72.21 ± 1.05), moisture content (3.96 ± 0.09-7.74 ± 0.13%), protein (2.72 ± 0.07-3.93 ± 0.06%), crude fat (0.11 ± 0.01-0.36 ± 0.04%), crude fiber (0.64 ± 0.03-1.22 ± 0.03%), carbohydrate (84.15 ± 0.24-88.26 ± 0.15%) and energy content (354.25 ± 0.57-370.02 ± 0.39 kcal/g). Total flavonoid content (21.44 ± 0.04-34.34 ± 0.03 mgQE/100g) and phenolic content (29.91 ± 0.01-71.46 ± 0.03 mgGAE/100g) was observed, while the highest retention of bioactive compounds was exhibited in Mehersagar cultivar's flour. In terms of appearance, fineness, taste, flavor, color, and overall acceptability, the dried banana flour of both the cultivars obtained from freeze-dried scored overall acceptability 8.04 ± 0.02 and 7.92 ± 0.17, respectively. The scanning electron microscopy analysis of the microstructure of flour granules from each sample revealed a diverse morphological configuration in particle size and shape. According to the findings of this study, the freeze-drying technology is superior to others, and the Mehersagar banana cultivar is more satisfactory in terms of quality characteristics. Moreover, the quality parameters of banana flour may facilitate the formulation of different flour-based gluten-free baked products and food supplements.

Effect of Pretreatments and Drying Methods on Physical and Microstructural Properties of Potato Flour

This study evaluated the effects of pretreatments (blanching (60 and 95 °C) and boiling) and drying methods (freeze-drying and oven drying) on the quality characteristics of potato flour derived from three potato varieties, namely, Shangi, Unica, and Dutch Robjin. The percentage flour yield, color, particle size distribution, flow characteristics, microstructural and functional properties of the potato flour were determined. Unica recorded the least peeling loss, while the Dutch Robjin variety had the highest. Color parameters were significantly affected (p < 0.05) by the pretreatments and drying methods. Freeze drying produced lighter potato flour (L* = 92.86) compared to the other methods. Boiling and blanching at 95 °C followed by oven drying recorded a low angle of repose and compressibility index, indicating better flow characteristics. The smallest particle size (56.5 µm) was recorded for the freeze-drying treatment, while boiling followed by oven drying had the largest particle size (307.5 µm). Microstructural results indicate that boiling and blanching at 95 °C, followed by oven drying resulted in damaged starch granules, while freeze-drying and low-temperature blanching (60 °C) maintained the native starch granule. Particle size and the solubility index of potato flour showed strong positive correlation. This study revealed that the pretreatments and drying methods affected potato flour’s physical and microstructural parameters differently, resulting in changes in their functionality.