Starch functionality in potato

B. Elliott1, J. M. C. Dang 1, C. Kaufman 2, W. Shadow 2, M. L. Bason 1

1 Perten Instruments Australia P/L, Warriewood, Australia
2 Perten Instruments Inc, Springfield IL, USA

The RVA offers the potential to measure starch properties that are a function of the combined composition and structure of potato.

The cooking process has a profound effect on the starch present in food. When potato is cooked, the starch loses its structural integrity as it gelatinizes and pastes. The degree to which the starch present in the sample has been transformed by the cooking process can be determined using an RVA ‘degree of cook’ method.

Aims

The goal of this work was to assess degree of cook on potato starch pasting properties.

Method

Retail samples of US Russet potatoes ‘Green Giant Selected Idaho Potatoes, Prime Size’ were obtained. The potatoes were scrubbed and washed in cold water, peeled and diced into approximately 0.75-inch (20 mm) cubes then pooled, mixed by hand and divided into 6 equal portions.

A ‘raw’ (0 minute) sample reference was prepared by grinding prepared potato in a manually operated food grinder twice. The sample was vacuum-sealed and placed in an ice water bath.

The remaining 5 samples were placed in a 93°C (200˚F) water bath and cooked for 1, 2, 4, 5, and 9 minutes, removed from the water bath with a slotted spoon, vacuum-sealed and placed in the ice water bath to cool. Cooled samples were ground twice in the hand-operated food grinder.

RVA sample to water ratio was adjusted to reflect the moisture content (80%) of the potatoes.

The samples were analysed in duplicate on an RVA-Super4, using 15 g of sample and 25 g of distilled water, shaken well for 15 seconds to disperse the sample, and the RVA ‘Extrusion 1’ test configuration (Table 4).

Data was collected on 2 days, from 2 bags of potatoes and the duplicate readings were averaged.

Table 4. Extrusion 1 Test Configuration.

Time Type Value
00:00:00 Temp. 25ºC
00:00:00 Speed 300 rpm
00:00:10 Speed 160 rpm
00:02:00 Temp. 25ºC
00:07:00 Temp. 80ºC
00:10:00 Temp. 80ºC
00:15:00 Temp. 25ºC

Idle temperature: 25 ± 1ºC
End of test: 20 min.
Time between readings: 4 sec.

Results

The degree of cook can be determined by assessing the reduction in peak, setback and final viscosities compared with those of raw samples (Figure 5, Figure 6, Figure 7).

Viscosity vs. Time in Ground Russet Potatoes Blanched for Various Times, then Ground, Over "Extrusion 1" Test Configuration, Using RVA Super4: 9/11/2008


Figure 5. RVA Results (Day 1)

Viscosity vs. Time in Ground Russet Potatoes Blanched for Various Times, then Ground, Over "Extrusion 1" Test Configuration, Using RVA Super4: 9/16/2008


Figure 6. RVA Results (Day 2)


Figure 7. Peak and Final Viscosities vs Cook Time for Potato Samples

Lower initial peak and final viscosities indicate a progressively higher degree of cook. The less-cooked samples display higher viscosity over the course of the profile. Thus, the RVA can be used to reliably assess the degree of cook in a par-cooked sample, ensuring a consistent degree of cook in potatoes delivered to an end user.

Conclusions

The RVA provides a convenient, rapid and objective means of estimating degree of cook in par-cooked potato samples.

Discussion

Other RVA potato applications include assessing textural properties of potato cultivars, predicting potato quality for baked and French fry applications, assessing degree of cook of dehydrated potato products as flakes, flours and granules used in the snack and baked foods industries and assessing heat, shear and acid stability of potato starches used in food applications.

Starch plays a prominent role in the determination of textural properties and potato starch has pronounced viscosity behaviours of the starch paste. Since food applications are based on these specific characteristics, a better knowledge of the starch quality of potatoes using RVA methods enables processing to take place in a more controlled manner.