A rapid and nondestructive fluorescence-based analyzer for monitoring the changes in deproteinized whey powder during storage

Deproteinized Whey (DPW) is a co-product obtained during ultrafiltration of whey. Subsequently, it undergoes unit operations like evaporation, crystallization, and spray drying resulting in a non-hygroscopic, free-flowing powder containing more than 80% lactose. Generally, DPW powder contains 2-7% protein, 3-4% moisture, and 8-11% ash. DPW is widely used as a replacer for sweet whey powder or lactose in bakery and confectionary applications, drink mixes, snack foods, and in certain ice-cream formulations. DPW powders may undergo chemical and physical changes such as caking, Maillard browning, and oxidation during storage. Amaltheys analyzer (Spectralys Innovation, Romainville, France) is a compact and portable fluorometer designed with 2 excitation light-emitting diodes at 280 and 340 nm. It is a rugged optical design with a low noise and enhanced UV sensitivity linear charge-coupled device. The objective of the present study was to use Amaltheys analyzer for monitoring Maillard changes during storage of DPW powder. For this purpose, 30 DPW samples were collected from a commercial manufacturer from different lots of production and storage periods. The FAST index (fluorescence of advanced Maillard products and soluble tryptophan) and the whey protein nitrogen index (WPNI) for DPW powders were measured by fluorescence- based Amaltheys analyzer. Additionally, colorimetric L*, a*, and b* values and water activity (aW) were also determined. The changes in terms of color and aW of DPW powder effected by storage time exhibited definite correlations. The L* values of DPW powders ranged from 85.86-92.02 and aW values ranged from 0.307-0.418. It was observed that lightness (L*) was negatively correlated (R = -0.71; P < 0.01) with aW of DPW powders. On the other hand, redness (a*) value was positively correlated (R = 0.82; P < 0.01) with aW of DPW powders. From the Amaltheys analyzer, the highest FAST index was observed as 362.24 for the powder with aW of 0.394. On the other hand, the lowest FAST index observed was 87.16 at aW of 0.381. It was also observed that FAST index was positively correlated (R = 0.46; P < 0.05) with redness (a*) value of DPW powders. A negative correlation (R = -0.89; P < 0.01) between FAST index and WPNI was observed. The FAST index and WPNI obtained using Amaltheys analyzer method is a simple, rapid, and low-cost method for the detection of Maillard changes in stored DPW powders.