Investigating the crystallinity of hard candies prepared and stored at different temperatures with low field-NMR relaxometry

Background: In this study, hard candies were produced by using sucrose, glucose syrup and water. They were cooked at different temperatures, changing from 135 to 145 degrees C with an interval of 2.5 degrees C. They were stored at different storage temperatures, which were 25, 4, -18 and -80 degrees C. Hard candies placed at room temperature were stored for 2 months. In order to understand the crystallization characteristics of the hard candies, time domain (TD) proton nuclear magnetic resonance (H-1-NMR) parameters of longitudinal relaxation time (T-1) and second moment (M-2) measurements were conducted. Moisture contents of the hard candies were determined by Karl-Fischer titration. X-ray diffraction experiments were also conducted as the complementary analysis. Results: Increasing cooking temperature increased the crystallinity and decreased the moisture content of the hard candies significantly (P <= 0.05). Furthermore, storage temperature and storage time had significant effects on the crystallinity of the hard candies (P <= 0.05). The results of T-1 and M-2 correlated with each other (r > 0.8, P <= 0.5) and both produced the highest value at the cooking temperature of 145 degrees C and storage temperature of 4 degrees C (P <= 0.05). The values of T-1 and M-2 were obtained as 245.9 ms and 13.0 x 10(-8) Hz(2), respectively, for the cooking temperature of 145 degrees C and storage temperature of 4 degrees C. Conclusion: This study demonstrated that the crystallinity of hard candies can be observed and examined by TD-NMR relaxometry, as an alternative to commonly used methods. (c) 2024 The Author(s). Journal of the Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.