Pectic hydrocolloids from steam-exploded lime pectin peel: Effect of temperature and time on macromolecular and functional properties.

Abstract

Previously, we showed the weight average molecular weight (M w) and intrinsic viscosity ([ƞ]) of pectic hydrocolloids recovered from steam‐exploded citrus peel were low, suggesting fragmentation due to process temperature and/or time‐at‐temperature. We have tested this hypothesis on a commercial lime pectin peel, washed to remove soluble sugars and dried for stabilization, using a static steam explosion system. We examined temperatures of 120–150°C at 1–3 min hold times. Galacturonic acid recovery and M w ranged from 22% to 82% and 142–214 kDa, respectively. Recovery of most major pectic sugars increased concomitantly with galacturonic acid as temperature and time‐at‐temperature increased. [ƞ] ranged from 1.75 to 6.83 dl/g. The degree of methylesterification ranged from 66.5% to 72.1%. Tan (δ) (Loss modulus/Storage modulus; G″/G′) values of sugar–acid gels for 120–140°C treatments were <1.0. Ideal optimization analysis, where time, [ƞ], and percent recovery were maximized, identified processing conditions that favor either increased [ƞ] or percent recovery. The results presented here support our hypothesis that temperature and time‐at‐temperature affect M w and [η] of the recovered pectic hydrocolloids. These results also demonstrate that manipulating either temperature or time‐at‐temperature enables the production of structurally varied populations of pectic hydrocolloids. Based on optimization analysis, commercially viable values of [ƞ] can be obtained while recovering approximately 50% of the pectic hydrocolloids.