Rheological behavior and storage studies of sprouted onion pastes from four onion varieties

Abstract

Objective: The study was carried out to investigate the rheological behavior and storage studies of sprouted onion pastes from four varieties (Punjab White, Punjab Naroya, PRO-6 and commercial). Methods: The storage study of paste samples from raw and sprouted onions packaged in polyethylene terephthalate (PET) bottles was carried out at room temperature (25 ± 1 °C) after thermally processing them at 80 °C for 15 min. All the paste samples were periodically analyzed for the change in quality characteristics viz, colour, pH, titratable acidity, TSS(∘B), TS (%), Water activity, Moisture (%), Total phenol content (mg/g), Total flavonoid content (mg/g), Total antioxidant capacity (mg/g), DPPH (%) and microbial count. The rheological properties of raw and sprouted onion paste samples were studied using Modular Compact Rheometer MCR-102 equipped with parallel plates geometry. Results and conclusions: Sprouted onion pastes were found to retain quality characteristics with lesser color changes, higher total phenolics, total flavonoids, antioxidant activity and microbial stability than raw pastes during storage. Storage period and its interactive effect with the variety and sprouting had significant (P < 0.05) effect on total antioxidant capacity, DPPH radical scavenging activity, L*, a* and b* values of onion pastes as revealed by multiple analysis of variance (MANOVA). The rheological studies of onion pastes depicted that the elastic modulus (G′) and viscous modulus (G″) decreased in all the sprouted paste samples which showed their decreased frequency dependency. In addition to the effect of sprouting the paste samples behaved either as a strong gel or weak gel depending on the concentration of the paste. This study showed that variety, sprouting and storage period resulted in onion pastes with different physicochemical composition, antioxidant potential and rheological characteristics. The intensity of change in quality parameters identified the opportunities of using sprouting process to enhance the storage stability and impart desirable rheological properties to onion pastes for various food applications.

Keywords

• Sprouted onion paste
• Storage
• Rheology
• Color change
• Variety