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 (H-NMR) parameters of longitudinal relaxation time (T) and second moment (M) 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 and M 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 and M were obtained as 245.9 ms and 13.0 × 10 Hz, 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. © 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.