The current work reports on isolation and physico-chemical characterization of floridean starch from three species of agarophytic macro red algae. As determined by 1 H-NMR spectroscopy, the average chain length and degree of branching frequency of this starch were 18 and 4.8, respectively. According to its amylopectin chain length distribution obtained by Dionex analysis, the crystalline polymorph of floridean starch from the red alga Gracilariopsis lemaneiformis was deduced to be C-type and this was further supported from its X-ray crystallographic pattern. Enzymatic analysis of its glucose 6-phosphate content showed that floridean starch had a low level of covalently linked phosphate (1 nmol per milligram starch) and this was further confirmed by 31 P-NMR. The absorbance peak of floridean starch with iodine occurred at 527-530 nm and the blue value was low (0.1), indicating the absence of amylose, which was confirmed by differential scanning calorimetry (DSC). Floridean starch exhibited low gelatinization temperature, low viscosity, high clarity and little or no retrogradation upon repetitive freeze-thaw cycles, as studied by DSC and rapid viscosity analysis (RVA). These results are discussed in light of the functional properties and the structure of floridean starch.

Amylolytic activity is widely distributed in plants. In potato leaves (Solanum tuberosum L.) the abundant amylolytic activity was found to be β‐amylase (EC 3.2.1.2, a‐1,4‐D‐glucan maltohydrolase). β‐Amylase from potato leaves was purified to homogeneity for study of enzyme characteristics. The purification steps included ammonium sulphate precipitation, anion exchange chromatography, affinity chromatography and gel filtration. The end product of α‐1,4‐glucan degradation was maltose. The protein is a 111‐kDa homo‐dimer with a subunit molecular mass of 56 kDa and a pl of 5.6. The pH‐optimum is 6.5 using p‐nitrophenylmaltopentaoside (PNPG5) as substrate. The optimal temperature for hydrolysis is at 40°C. The enzyme is unstable at temperatures above 40°C. The Knt‐value for PNPG5 is 0.73 mM and the activity is inhibited by cyclodextrins. At a concentration of 1 mM, β‐cyclodextrin is a stronger inhibitor than α‐cyclodextrin (68 and 20% inhibition, respectively). Branched glucans (e.g. starch and amylopectin) are superior substrates as compared to long, essentially unbranched glucans (e.g. amylose). This study of the catalytic properties of β‐amylase from potato leaves indicates the importance of β‐amylase as a starch degrading enzyme.

Purification of α-1,4-glucan lyase from red algae and fungi has previously been reported. The α-glucan lyase converts α-glucans to 1,5-anhydro--fructose. In this study, an endophyte was detected between the algal cells of Gracilariopsis sp., but not penetrating the cell walls. Histological staining was consistent with the endophyte being fungal and immunohistochemistry revealed that it possessed an α-1,4-glucan lyase differing from that of the host. The endophyte α-glucan lyase was recognized by antisera against both fungal and red algal α-glucan lyases, whereas the α-glucan lyase found in the algal tissue was recognized only by the antisera against algal α-glucan lyase. The lyases occur independently in the host and in the endophyte, and were sometimes detected simultaneously. The endophyte was only observed in Gracilariopsis sp. collected in China ; no endophyte could be detected in Gracilariopsis sp. from California or in Gracilaria chilensis.