Studies on the extraction and characterization of pectin and bitter principles from New Zealand grapefruit and Philippine calamansi : a thesis presented in partial fulfilment of the requirements for the degree of Master of Technology in Food Technology at Massey University

Abstract

A study was conducted to determine the presence of bitter components in NZ grapefruit and Philippine calamansi; describe the effect of maturity on the bitter components and other chemical constituents of grapefruit; reduce the bitterness of grapefruit juice by adsorption on polyvinylpyrrolidone; and to extract and characterize pectin from grapefruit peel. Naringin (995 PPm), narirutin (187 ppm), and limonoids (7.9 ppm) were detected in NZ grapefruit juice concentrate (27° Brix). Naringin was not detected in the calamansi juice, and limonin was detected at the level of 10.5 ppm in juice containing 5% crushed seeds. Maturation of the grapefruit caused an increase in pH from 3.00 to 3.50, an increase in total soluble solids from 10.8 to 14.4 with a decline to 13.5° Brix later in the season, a steady fall in acidity from 2.50 to 1.31 g citric acid/100 mL, and a continuous rise in the Brix/acid ratio from 4.2 to 10.3. Juice yield fluctuated throughout the season. Ascorbic acid remained fairly steady in the early and mid-season fruit but decreased in the late-season fruit. Naringin content was highest at the beginning of the season and fluctuated throughout the season. Naringin content in the grapefruit peel remained constant as the fruit matured. Narirutin was detected in the early-season fruit but disappeared later in the season. Limonoid content in both unpasteurized and pasteurized juices decreased with ripening. The use of polyvinylpyrrolidone significantly reduced naringin in grapefruit juice by up to 78.1% and limonin by up to 17.5% depending on the amount and reaction time of the adsorbent. A loss of 23.1% in ascorbic acid occurred with 5% PVP with a reaction time of 1 h. Pectin extraction at 85°C and the use of acidified isopropyl alcohol yielded a product with the following characteristics: 8.9% yield; 1.3% moisture content; 1.9% ash; 759 equivalent weight; 9.2% methoxyl content; 82.2% anhydrogalacturonic acid; 63.2% degree of esterification; 4.2 intrinsic viscosity; 89,362 molecular weight and setting time of 0.55 minute.