INTERVENCIONES PSICOTERAPÉUTICAS:
2.10. RESPUESTAS EMOCIONALES:
A viscometer (Rapid Visco Analyzer, RVA-4, Newport Scientific, Warriewood,
Australia) was used for conducting liquefaction of corn slurries. During liquefaction, a viscosity profile was produced for each of the samples. Slurries were comprised of 25 g (db) ground corn combined with deionized water to reach a solids concentration of 36% w/w.
Corn slurry preliquefaction viscosities were measured before enzyme addition. Samples were placed in the RVA, with constant stirring at 80 rpm and a temperature of 32°C for 10 min.
35
This period provided time for stabilizing and recording preliquefaction viscosity values. After this measurement, slurry pH values were adjusted to the optimal level for each particular treatment. Alpha-amylases AA-1 and AA-2 were added to treatments that included no amylase corn. Each enzyme was added at the upper limit of the dosage recommended by the
manufacturer (0.31 mg/g (db) corn for AA-1 and 0.24 mg/g (db) corn for AA-2).
In the first stage of liquefaction, corn slurry samples were heated rapidly from room temperature to 32°C. The temperature was increased at 18°C/min until reaching 85°C and kept for 90 min to allow for starch gelatinization and hydrolysis. To measure final viscosities, slurries were cooled to 32°C at a rate of 5°C/min and held for 10 min.
4.2.2.3. Experimental Design and Data Analysis
Three treatments were evaluated: one of 15% alpha-amylase corn and 85% yellow dent corn and two of 100% yellow dent corn (Table 4.1). No enzymes were added to the treatment with 15% amylase corn, as this variety contained alpha-amylase. AA-1 and AA-2 were each assigned to one of the 100% yellow dent corn treatments.
Table 4.1. Treatments used to evaluate the effect of different alpha-amylase sources on
final liquefaction viscosity of corn slurries at high solids (36% w/w). Corn Composition
[% amylase / % yellow dent]
Alpha-Amylase Added
15/85 None
0/100 AA-1
36
Liquefactions were conducted with three replications. Experimental conditions, such as temperatures, stirring speed, pH and alpha-amylase dose, were constant for each treatment. RVA viscosity data were collected through computational software (TCW3, Perten Instruments, Sidney, Australia). Viscosity profiles were evaluated to determine effects of alpha-amylase sources on final liquefaction viscosity of corn slurries at high solids (36% w/w). Initial, peak, setback, final and breakdown viscosity means were analyzed statistically using SAS (SAS Institute, Cary, NC). ANOVA and LSD tests with p<0.05 were used to compare means among treatments.
4.3. Results and Discussion
Corn slurry viscosity profiles were evaluated using a 90 min liquefaction process (Fig. 4.1). During initial heating, the temperature increased from 32 to 85°C. The heating process in excess water caused starch granules to hydrate progressively and swell (Tester et al 2006). This phenomenon resulted in a higher volume fraction of granules in the medium and a corresponding increase in slurry viscosity (Bagley and Christianson 1982). Starch granules swell to a point at which their granular structure is lost and gelatinization occurs. After this occurs, alpha-amylase is able to digest starch granules. Exogenous and endogenous alpha-amylases used in these experiments approached their optimum action range as the temperature increased to 85˚C. Amylolytic effect on slurry viscosities can be observed in Fig. 4.1. Viscosities increased with temperature and peaked as the system reached 85˚C. As the process continued, the enzymes were able to break down amylose and amylopectin chains released from starch granules. This process led to a progressive viscosity reduction, reaching values from 100 to 200 cP.
37
Figure 4.1. Liquefaction viscosity profiles obtained from Rapid Visco
Analyzer, through TCW3 (means of three observations).
After completing a 90 min liquefaction period at 85˚C, system temperature was decreased to 32˚C. Upon cooling, the corn slurry samples experienced a final viscosity increase, which was caused by a phenomenon called retrogradation, in which molecular chains reorganize in an ordered structure (Sandu and Singh 2007). The treatments at 100% conventional corn (liquefied with AA-1) and at 15% amylase corn achieved similar final viscosities (Fig. 4.2).
Comparatively, the treatment at 100% conventional corn, liquefied with AA-2, reached the highest viscosity at the end of the process. Therefore, starch hydrolysis was adequate in the first two cases; in the latter, polysaccharides left in solution recombined, causing an increase in the final viscosity. 0 10 20 30 40 50 60 70 80 90 100 0 2000 4000 6000 8000 10000 12000 14000 16000 0 20 40 60 80 100 120 T em per at ur e [˚ C ] V isc osi ty [ cP] Time [min] 15% amylase-corn / 85% conv. 100% Conv. + AA-1 100% Conv. + AA-2 Temperature
38
Figure 4.2. Initial, peak, breakdown, setback and final viscosity values observed during
liquefaction (means of three observations). Bars are ±1 standard deviation of the mean.
Initial, peak, breakdown, setback and final viscosities observed in the three treatments are depicted in Fig. 4.2. The corn mixture with 15% amylase corn had higher initial viscosity than that of only yellow dent corn. The AA-2 treatment had the lowest viscosity peak, followed by AA-1 treatment. Maximum peak viscosity was reached by the treatment with 15% amylase corn. Singh et al (2006a) also observed this peak. They suggested that during the initial phase of the liquefaction process, the endogenous alpha-amylase contained in amylase corn was not entirely available. Eventually, the enzyme is released and activated becoming able to depolymerize amylose and amylopectin chains and reducing slurry viscosity. In control treatments, alpha- amylase was readily available in the slurry, as it was added externally in liquid form.
Treatments with 15% amylase corn had the highest breakdown viscosity (16400 cP). Despite developing the maximum peak among all treatments, the large breakdown capability of
0 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
Initial Peak Breakdown Setback Final
V isc osity [ cP] 15% amylase-corn / 85% conv. 100% conv. + AA-1 100% conv. + AA-2
39
amylase corn resulted in similar viscosities to those reached by AA-1 and AA-2 treatments during liquefaction.
Table 4.2. Viscosities observed during liquefaction of samples
with 36% w/w solids at 85˚C (means of three observations). Corn Composition [% amylase / % yellow dent] Alpha- Amylase Added Viscosity [cP]
Initiala,b Peaka Breakdowna Setbacka Finala
15/85 - 1700 a 16500 a 16400 a 400 a 500 a 0/100 AA-1 900 b 12700 b 12700 b 700 a 700 a 0/100 AA-2 900 b 9300 c 9000 c 1800 b 2000 b
LSD 100 3200 3200 500 500
a Means followed by the same letter in the same column are not different. b Initial viscosity values were recorded before the addition of enzymes.
Setback viscosities were not different for AA-1 and 15% amylase corn treatments. However, AA-2 treatment had the largest setback viscosity, resulting in the highest final value. Final viscosities of 15% amylase corn and AA-1 treatments were not different.
4.4. Conclusions
The liquefaction of corn slurries at 36% w/w solids with amylase corn inclusion level of 15% resulted in peak viscosities of 16500 cP, higher than treatments with conventional alpha- amylases. High peak viscosities observed in amylase corn treatments may limit the applicability of this technology at commercial scale.
40
Samples with 15% amylase corn had final liquefaction viscosities of 500 cP. Inclusion of 15% amylase corn is a viable alternative as a source of alpha-amylase and as a viscosity reducing agent. Application of this technology resulted in similar or lower final viscosities than with exogenous alpha-amylases. The high viscosity reducing capacity of amylase corn may allow processing slurries at higher solids concentration and reduce energy and water consumption.
41