Optimization of Drying Conditions and Nutritional Characterization of Lotus Stem Flour

Postharvest management of lotus stems (Nelumbo nucifera) is critically underemphasized in the food industry, leading to significant quality degradation and postharvest losses due to mechanical damage during handling, transportation, and valorization. This study aimed to optimize drying conditions through various pretreatments to enhance the processing and valorization efficiency of lotus stems and to characterize lotus stem flour in terms of its proximate composition, functional properties, and amino acid profile. This is the first study to optimize the drying conditions of lotus stem flour using citric acid and potassium metabisulfite (KMS) pretreatments, ensuring better retention of quality attributes. Lotus stems exhibit substantial variability, with weights ranging from 32.55 to 245.65 g, length from 18.00 to 44.35 cm, and width from 1.30 to 3.80 cm. Lotus stem slices dried at 70°C for 2 h yielded the highest percentage (26.50%), although higher temperatures generally resulted in decreased yields due to moisture loss and structural changes. The color attributes of lotus stem flour are affected by the drying temperature and anti-browning agents. The use of citric acid improved redness and yellowness, whereas potassium metabisulfite affected the color based on the concentration. Lotus stems pretreated with 2% KMS improved the lightness (L) by up to 18% (from 71.85 to 85.25), while the samples treated with 2% citric acid increased redness (a*) by approximately 57% (from 4.20 to 6.60) and yellowness (b*) by 33% (from 14.60 to 19.45), indicating enhanced color retention. Moreover, the lotus stem flour is characterized by moisture (6.30%), protein (7.60 g), carbohydrate (70.90 g), and fat (1.45 g), providing an energy value of 326.77 Kcal. It also contains appreciable amounts of essential minerals, including calcium, potassium, and magnesium, as well as negligible levels of toxic heavy metals. Flour is notable for its essential amino acids, particularly threonine, lysine, and leucine, and includes a range of nonessential and conditionally essential amino acids, contributing to its comprehensive nutritional profile. These findings highlight the potential of lotus stem flour as a functional ingredient for the food industry, particularly in the development of nutritionally enriched and shelf-stable products.