Effects of High Hydrostatic Pressure Versus Heat Treatment on the Quality and Rheological Properties of Low-Sugar Citrus Jam

In this study, low-sugar citrus jam was prepared from either ‘Jiuyuehong’ navel orange or Yichang tangerine by two different methods: high hydrostatic pressure at 500 MPa for 10 min, and heat treatment (water bath heating 100 ℃ for 30 min). The effects of high hydrostatic pressure and heat treatment on the quality and rheological properties of low-sugar citrus jam were investigated by analyzing physicochemical, sensory, color, rheological and texture properties. The results showed that high hydrostatic pressure and heat treatment reduced the content of total phenols in navel orange jam by 13.67% and 7.34% and in tangerine jam by 41.41% and 15.32%, respectively. Compared with the untreated citrus jam, heat treatment caused significant browning in both citrus jams, with total color difference (∆E) greater than 2. High hydrostatic pressure treatment significantly increased the brightness (L*) of the two citrus jams (P < 0.05). All four citrus jam samples were shear-thinning pseudoplastic fluids, and their storage (G’) and loss (G”) moduli increased with an increase in oscillation frequency; G’ was always greater than the corresponding G”, which is characteristic of an elasticity-dominant viscoelastic body. As far as navel orange jam was concerned, in the frequency range of 0.1–100 rad/s, G’ was largest in the heat treatment group (757.2–4390.5 Pa), medium in the high hydrostatic pressure group (375.5–2641.5 Pa), and smallest in the untreated group (177.25–973.95 Pa). A similar trend was observed for tangerine jam. In addition, compared to those prepared by heat treatment, high hydrostatic pressure treated citrus jams had lower firmness, stickiness and chewiness, and a more delicate mouthfeel. In conclusion, the quality of citrus jam prepared by high hydrostatic pressure is better. The results of this study can provide a reference for the development of new jams.