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 °C with an interval of 2.5 °C. They were stored at different storage temperatures, which were 25, 4, −18 and −80 °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 ( 1 H‐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 °C and storage temperature of 4 °C ( P ≤ 0.05). The values of T 1 and M 2 were obtained as 245.9 ms and 13.0 × 10 −8 Hz 2 , respectively, for the cooking temperature of 145 °C and storage temperature of 4 °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.