1. (malting and extrusion) processing
Digestibility, TOTAL PHENOLIC CONTENT AND ANTIOXIDANT ACTIVITY OF PEARL MILLET (Pennisetum glaucum ) as affected by combination
(malting and extrusion) processing
A.O. OBILANA1, B. ODHAV2, J.R.N. TAYLOR3
1. Department of Food Technology, Cape Peninsula University of Technology, P.O. Box 1906, Cape Town
2. Department of Biotechnology and Food Technology, Durban University of Technology 43 Centenary Road Durban
3. Department of Food Science, University of Pretoria, Lynnwood Road, Pretoria.
ABSTRACT
DATA ANALYSES
RESULTS AND DISCUSSION
RESULTS AND
Data obtained was analysed by analysis of variance followed by the least significant difference test (LSD test). Correlations were evaluated at the 1% and 5% significance level. All statistical analyses were carried out using the SPSS Statistics program 2008 version
In this experiment, a new ready-to-eat meal was developed with pearl millet (Pennisetum glaucum), using malting and extrusion processing alone and in combination. Samples included raw pearl millet, extruded raw pearl millet, extruded malted pearl millet and extruded (50% raw + 50% malted) pearl millet. The effects of the processes on the digestibility, total phenolic contents (by Folin-Coicalteau) and antioxidant activity (by oxygen radical absorbance capacity (ORAC), trolox equivalent antioxidant capacity (TEAC) and ferric ion reducing antioxidant power (FRAP)), physical properties (expansion ratio (ER), water absorption index (WAI) and water solubility index (WSI)), were assessed and statistically analysed using one way ANOVA. The processes had a significant effect (p ≤ 0.05) on ER, WAI and WSI; protein and starch digestibility as well as antioxidant activity (FRAP), but not on total phenolic content and antioxidant activity (TEAC and ORAC).
Functional, healthy, neutraceuticals, convenient, these are a few buzz words relating to customer demands that are driving change in the food industry currently. Others include but are not limited to, probiotic, prebiotic, low glycemic index, to name a few. In a bid to meet these consumer demands, the food industry is directing new product development towards the area of functional foods and functional food ingredients.
Cereal grains are important sources of energy, protein, dietary fibre, minerals, vitamins and phytochemicals such as phenolic acid, phytic acids, lignans and phytoestrogens (Slavin et al., 1999). However, the nutritional quality of cereals and the sensorial properties of their products are sometimes inferior or poor in comparison with milk and milk products. The reasons behind this are the lower protein content, the deficiency of certain essential amino acids (lysine), the low starch availability, the presence of determined antinutrients (phytic acid, tannins and other polyphenols) and the coarse nature of the grains (Chavan and Kadam, 1989).
In recent times, however, some of these “antinutrients” (fibre, polyphenols) have been found to have functional / health benefits when consumed and as such have become the focus of numerous researches to determine their role in human health.
The objective of this research was to determine the effects of combination processing (malting and extrusion) on some physical properties (ER, WAI, and WSI), starch and protein digestibility as well as the total phenolic content (TPC) and antioxidant activity of millet (Pennisetum glaucum) during the production of a ready-to-eat (RTE) pearl millet based food product.
The treatments used had significant (p ≤ 0.05) effects on the physical properties of the millet as shown in figure 5.
TPC was not significantly (p ≤ 0.05) affected by the different processing methods (fig 6). Antioxidant activity by the ORAC and TEAC methods were not significantly affected by the different processing methods. Antioxidant activity by the FRAP method was significantly (p ≤ 0.05) higher 7.89 µmole/g than the raw samples for the extruded samples, but significantly lower 3.56, 3.28 and 4.58 µmole/g than the raw sample for the MM, ERMM and EMM samples respectively.
Starch and protein digestibility were also significantly (p ≤ 0.05) affected by the treatments (fig 7), with an average increase of 8.1% in starch digestibility when compared to the raw grain. There was also a significant increase in protein digestibility with the treatments, although a lower percentage digestibility was noted for the mixture. The increase in digestibility could have been as a result of treatments breaking down starch and proteins into smaller sub units which are more readily digestible.
There was a significant (p ≤ 0.01) correlation between the physical properties (ER, WAI and WSI), but neither of these showed a significant (p ≤ 0.05) correlation with starch digestibility (fig 1).
The correlation between TPC, ORAC and TEAC was positive and significant (p ≤ 0.01) and that between TPC, FRAP and TEAC was also positive and significant (p ≤ 0.05), but the correlation between FRAP and ORAC though positive, was not significant (p ≤ 0.05). The fact that antioxidant activity by FRAP was significantly (p ≤ 0.05) different from antioxidant activity by TEAC and ORAC, may be due to the fact that FRAP determines antioxidant activity by a different mechanism to that used by TEAC and ORAC. It can be seen in figure 6 that heat processing seems to increase antioxidant activity by the FRAP method, an effect not noticed when measured by the other two methods.
Figure 5: Physical properties of raw and processed pearl millet
INTRODUCTION
Fig 1: Flow Diagram for Treatments 1 - 5 b
Figure 6: Total phenolic content and antioxidant activity of raw and processed pearl millet
Fig 2: Pearl Millet (Pennisetum glaucum)
Figure 7: Protein and Starch Digestibility of raw and processed pearl millet
Fig 3: Malted pearl millet
Table 1: Pearson’s correlation between physical properties and digestibility; TPC and antioxidant activity
OBJECTIVE
CONCLUSIONS
Malting and extrusion either alone or in combination can be used to process pearl millet producing a convenient food product with improved starch digestibility, without significantly affecting the total phenolics content and antioxidant activity as measured by TEAC and ORAC. More work needs to be done to determine if this antioxidant activity is conferred to the body when the food product is consumed.
Fig 4: Extruded pearl millet
METHOD AND MATERIALS
In total there were four (4) processes (Process 1 (Control), 2, 3 and 4) administered to the raw material as shown in the flow diagrams in figure 1. All samples were stored in a full barrier bag in a cold room set at 5oC until required for further processing or analyses. Samples prepared included; raw millet (RM), extruded millet (EM), malted millet (MM), extruded malted millet (EMM) and extruded raw + malted millet (ERMM) A B
REFERENCES
CHAVAN, J. K. & KADAM, S. S. (1989) Nutritional improvement of cereals by sprouting. Critical Reviews in Food Science and Nutrition Toxicology, 28,
SLAVIN, J. L., MARTINI, M. C., JR, D. R. J. & MARQUART, L. (1999) Plausible mechanisms for the protectiveness of whole grains. American Journal of Clinical Nutrition, 70, 459S-463S.
Fig 5: Raw Pearl millet meal (hammer mill) (A), Extruded pearl millet meal (roller mill) (B)
**. Correlation is significant at the 0.01 level (2-tailed).
*. Correlation is significant at the 0.05 level (2-tailed).
() P values