Maltose assay kit

The total starch in the banana pulp was quantified enzymatically using the Starch Assay Kit (Sigma‐Aldrich Shanghai Trading Co Ltd, Shanghai, China). Glucose is phosphorylated by adenosine triphosphate (ATP) in the reaction catalysed by hexokinase. Glucose‐6‐phosphate (G6P) is then oxidized to 6‐phosphogluconate in the presence of nicotinamide adenine dinucleotide (NAD) in a reaction catalysed by glucose‐6‐phosphate dehydrogenase (G6PDH). During this oxidation, an equimolar amount of NAD is reduced to NADH. The consequent increase in absorbance at 340 nm is directly proportional to the glucose concentration.
The total soluble sugars were estimated by anthrone reagent. An aliquot (1 mL properly diluted) of supernatants was taken in the test tube, mixed with 5 mL of anthrone regent and the mixture was heated in boiling water bath for 10 min followed by cooling. Optical density was read at 620 nm, and the results were calculated using standard curves for sucrose. With the Maltose Assay Kit (Sigma), maltose is converted to two glucose units via a‐D‐Glucosidase. Glucose is further oxidized, resulting in a colorimetric (570 nm) product, proportional to the maltose present. Glucose was measured using the Glucose (HK) Assay Kit (Sigma) according to the manufacturer's instructions.

Concentrations of glucose and maltose were determined spectrophotometrically by using the Glucose (HK) Assay Kit (GAHK-20, Sigma-Aldrich) and Maltose Assay Kit (MAK019, Sigma-Aldrich), following the manufacturer's instructions. Amino acids were measured using the EZ:faast™ GC-MS free amino acid analysis kit of Phenomenex which was previously used in amino acid uptake profiling of S. lividans [33 (link)]. Derivatization and preparation of samples were following the protocol, and amino acids were measured by GC-MS (QP-2010 Ultra, Shimadzu). The Zebron ZB-AAA capillary column (10 m × 0.25 mm) supplied with the test kit was used. Helium was used as the carrier gas at a flow rate of 1.2 ml min⁻¹. The GC-MS conditions were as follows: the injection temperature, 300°C; the inlet line temperature, 320°C; the ion source temperature, 240°C; initial oven temperature, 110°C; held for 0.5 min then increased to 310°C at 30°C min⁻¹, held for 0.5 min. The scan range was 45–450 (3.5 scans s⁻¹). Under these conditions, a 1 µl sample was injected in a split (1 : 15) mode.