Lynne Wong's PhD thesis

6.3 TOTAL SOLID SURFACE AREA AVAILABLE FOR HYDROPHILIC
BINDING IN ADSORPTION
The solid surface area was determined from the monolayer moisture content by using the
following equation (Mazza and Le Maguer, 1978):
A = m o N A A m /m w = 35.42 m o
where A is the solid surface area (m 2 g solids -1 ), m o is the monolayer moisture content
(% db), m w is the molar mass of water (18.02 g mol -1 ), N A is Avogadro’s number (6.022 x
10 23 molecules mol -1 ), and A m is the area of a water molecule (1.06 x 10 -19 m 2 molecule -1 ).
Since the GAB was found to be a good fit to the experimental adsorption data, the m o value
calculated from the GAB equation was used to estimate the total solid surface area A.
The results of the total solid surface area A calculated are also presented in Table 6.2. In
general, A decreased with increased temperature. Stalk pith and dry leaf fines were among
those components which had high surface area for hydrophilic binding.
Arslan and Toğrul (2005) found in their study of moisture adsorption of macaroni, the total
available surface area for hydrophilic binding decreases with an increase in temperature.
This is also true for most sugar cane component parts aged 52 and 36 weeks except for rind
fibre and rind fines of both ages, top fibre, dry leaf fibre and green leaf fines aged 52
weeks and dry leaf fines aged 36 weeks.
The values found for the sugar cane fibres vary from 100 – 200 m 2 g solids -1 , which are
much lower than the 200 – 300 m 2 g solids -1 found for macaroni by Arslan and Toğrul
(2005), and similarly for quinoa grains by Tolaba et al. (2004), but higher than in goat
meat (Singh et al., 2006), kheer (Kumar et al., 2005) and chhana podo (Rao et al., 2006),
all about 80 m 2 g solids -1 .
As the temperature increased from 30 to 60 °C, the number of adsorbed monolayers, the
percentage of bound water and the surface area of adsorbent decreased. This may be due
to the reduction in sorption of water with increasing temperature in the low water activity
range.
Noguchi (1981) reported that hydrophobic hydration of biopolymers melts off rapidly as
the temperature increases.
246