Cell wall modifications during cooking of potatoes and sweet potatoes

Abstract

Sweet potato (Ipomoea batatas L) tissue, when cooked at 70°C to activate b-amylase and break down starch, takes on a distinctive ®rm, brittle texture and does not show the cell separation that occurs in, for example, cooked potato (Solanum tuberosum L). Similar cooking conditions increase ®rmness in other plants by activating pectin methyl esterase which de-esteri®es pectic polysaccharides and protects them from thermal depolymerisation. We therefore isolated cell walls from both potatoes and sweet potatoes cooked at 70°C and 100°C and determined the remaining degree of methyl esteri®cation of their pectins. Pectins from both species were demethylated to a similar extent at 70°C and 100°C. Since cooking sweet potato at 100°C induced cell separation and softening, it is concluded that b-amylase is rapidly inactivated at that temperature and swollen starch distends and separates the cells, whereas the ®rm texture obtained by cooking that species at 70°C is not the result of pectin demethylation but is caused by the breakdown of starch to oligomers that can escape from the cell.

Microstructure and creep-recovery characteristics of achu (a taro based paste) made from freeze dried taro chips as affected by moisture content and variety

“…This has been generally attributed to the beliminative degradation of pectic polysaccharides which have long been considered to play a major role in cell adhesion. Predominance of cell separation was reported by Binner et al (2000) to result in mealy or floury texture. In the present study, the time required for total cells rupture was 14.5, 18, 21 and 37 min for the varieties MBA, RI, MF and WC, respectively.…”

Textural properties of potatoes (Solanum tuberosum L., cv. Monalisa) as affected by different cooking processes

“…The texture of cooked potatoes has been the subject of study of many research papers (Thybo et al, 1998;Truong et al, 1998;Binner et al, 2000;Kaur et al, 2002;Van Dijk Abu-Ghannam and Crowley, 2006;Chiavaro et al, 2006). The texture of cooked potatoes has been associated with starch and pectic substances, dry solids content, specific gravity, amylase, sugars, proteins and the total nitrogen content of the tuber (Linehan and Hughes, 1969;Reeve, 1972).…”

“…As such, the properties of starch and the changes which occur in these properties during cooking should be considered when explaining the variations in texture. Textural changes in cooked potatoes are mainly associated with the gelatinisation and retrogradation behaviour of starch (Kaur et al, 2002) and with enzymatic and nonenzymatic changes in pectin (Binner et al, 2000;Van Dijk et al, 2002). Enzymatic degradation of cell wall pectin is catalysed by different pectinases, such as pectinmethylesterase (PME) and polygalacturonase (PG) (Van Buren, 1979).…”

The synergistic effect of moderate heat and pressure on the physical properties and pectic substances of potato tissue

“…Most probably, none of these theories alone can explain the phenomenon and more than one mechanism seem to be involved. Binner et al. (2000) showed that preheating increases firmness in plant tissues by activating PME, the de‐esterification of pectic polysaccharides protecting them from thermal depolymerisation.…”