Comparison of rheological models to explain flow behavior of green coconut pulp: effect of maturation stage and temperature

Abstract

Green coconuts are harvested from six (young coconuts) to ten months (mature coconuts) after flowering. Green coconut pulp (GCP) is a byproduct of coconut water processing that presents foaming and emulsifying capacity and can be employed as a plant based alternative in different food products. Determining its rheological properties at different temperatures furnishes useful processing information. Rheological flow curves were obtained with a controlled stress rotational rheometer from (0.01 to 300 s−1) at temperatures from 20 to 80 °C. Young and mature GCP samples presented shear-thinning behavior represented by the Power Law and Herschel-Bulkley models. The models were compared by a Monte Carlo Markov Chain method that converged with small simulation errors, indicating its stability and that both models adequately described the data. The comparison of the Akaike’s information criterion indicated that for young GCP the Herschel-Bulkley model is preferable while for mature GCP the Power Law model is adequate. The apparent viscosity of mature GCP was approximately 100 times higher than for young GCP samples within the same range of shear rates. Mature GCP consistency coefficient variation with temperature was described by an Arrhenius model. The apparent viscosity (µap) of young GCP decreased with temperature up to 50 °C, then increased, particularly at low shear rates. For mature GCP samples apparent viscosity decreased with temperature rise. The change in composition (particularly lipids content) is probably responsible for the observed flow behavior at different maturation stages.