EFFECTS OF PROCESSING TECHNIQUES ON CHEMICAL, FUNCTIONAL AND MICROBIAL PROPERTIES OF TWO VARIETIES OF LIMA BEAN (PHASEOLUS LUNATUS) AND MAIZE (ZEA MAYS) FLOURS AND SENSORY PROPERTIES OF THEIR PRODUCTS

Abstract

This study evaluated  the effects  of different  domestic  food processing  techniques  on  the nutrients, antinutrients, food toxicants composition, functional properties, microbial types and sensory properties of food products based on two varieties of lima bean (Phaseolus lunatus). Black and dark red varieties of lima bean were purchased, cleaned, cooked, soaked, dehulled,

germinated, fermented and milled into fine flours. Both the unprocessed and processed flours were analysed for microflora composition, chemical, functional and sensory properties using standard methods. The 48h fermented maize and lima bean flours that had traces of hydrogen cyanide (HCN) were selected because they had the best nutrient profiles in a ratio of 70:30 (protein basis) to formulate composite flours for moi-moi and akara production. Two local dishes (oshoto and ikpaki) were prepared from whole unprocessed lima bean and maize. The data were statistically analyzed using percentages, means and standard deviation. Duncan’s new multiple range test was adopted to separate and compare means. The 3 and 9h soaking as well as 48h  fermentation  increased protein in black lima bean (26.07, 26.68 and 32.67%, respectively). On the other hand, dehulling and cooking, 6 and 9h soaking, 72, 96 and 120h germination  as well as 48h fermentation  increased  protein  in dark red lima  bean.  These treatments equally decreased fat, ash and fibre in both varieties. Carbohydrate was increased in  both  varieties.  Dehulling,  cooking  and  24h  fermentation  increased  zinc  in  black  and decreased it in dark red variety. Processing decreased copper, iron and phosphorus in black lima bean. Dark red lima bean whose cooking water was drained and replaced had decreases in copper   relative to the control.  Iron and phosphorus decreased regardless of treatments. Treatments slightly increased folate in dark red lima bean flours except for 72h germinated and 48h fermented samples. Phytate, hydrogen cyanide (HCN), trypsin inhibitor and saponin were reduced in both varieties. Tannins and haemagglutinin levels increased in germinated samples.  Foam and oil absorption  capacities decreased in both varieties due to treatment. Water absorption capacity increased in both varieties except for the black variety fermented for 24h and  120h germinated dark red variety.  Emulsion capacity decreased in black variety except  for  9h  soaked,  72  and  120h  germinated  flours  relative  to  the  control.  Emulsion capacity increased in red variety except for the 48h fermented sample. Protein decreased in both composites relative to their controls, except for the 48h fermented black lima bean and maize blend. Fat increased in black lima bean and maize flour blends, except for equal value for  the  cooked  composite  relative  to  the  control  (1.60%).  Ash  and  fibre  decreased  in composites of both varieties. The decrease was much more in dark red variety. Carbohydrate values  for  the  composites  increased  regardless  of  varietal  differences.  Mineral  levels  in composite flours differed (P < 0.05). Zinc and copper increased in both varieties relative to their  controls  except  for  Cu  of  96h  germinated  and  48h  fermented  black  lima  bean composites.  Iron increased in the composites of both varieties except for the cooked and 72h fermented black lima bean composite. Phosphorus increased in black composites except for the  cooked  and  72h  fermented  composites.  Both  moi-moi  and  akara  from  48  and  72h fermented  varieties and 48h fermented  maize blends had increased  protein relative to  the control.  Fat, fibre, ash and carbohydrate  of moi-moi  and akara from both  varieties were slightly higher than their controls. Calcium, magnesium, potassium, phosphorus and iron of both  products  had  increases,  except  for a few products.  Cooking  and  dehulling  of  both varieties   caused   drastic   decrease   in  pathogenic   microflora   than   the   other   methods. Organoleptic attributes and general acceptability of moi-moi and akara from both varieties improved  due  to  processing.  The  protein,  fat,  ash,  fibre  and  carbohydrate  content  of traditional dishes (oshoto) prepared with cooked whole lima bean and maize were higher than those cooked without maize (ikpaki) regardless of varietal differences. Calcium, magnesium, potassium, phosphorus and iron  values for traditional dishes containing maize were higher than in the dishes prepared without maize. Organoleptic attributes of dishes from blends of lima bean and maize were slightly lower than the dishes prepared without maize. Domestic food  processing  techniques,  especially  cooking  and  fermentation  increased  macro  and micronutrients,   decreased  antinutrients  and  food  toxicants  in  lima  bean.   Organoleptic attributes of both dishes and products were highly acceptable. Processed lima bean flours and products have diversified food use to reduce food insecurity.

CHAPTER ONE

INTRODUCTION

1.1      BACKGROUND OF STUDY

In  Nigeria,  a  lot  of  under  exploited  plant  food  crops  with  promising  nutritional potentials exist. Lima bean is one of the under exploited food crops with nutritional and food industry processing potentials. Lima bean is among the lesser known legumes in the southern part of Nigeria. The food crop is one of the traditional staples that in the most recent decades was neglected. However, the neglect is attributed to  difficulties  in production, processing, preparation, utilization and negative image attached to it as “poor man’s food”. Lima bean has longer cooking time, especially as  compared with other legumes. This longer cooking time phenomenon is a particular drawback for its cultivation and food use. It is imperative to investigate the positive attributes of this important food legume mostly its nutrient potentials.

Legumes as protein-rich crops are important source of protein for human food  and animal feed. In 1972-1974, legumes contributed 7% to the total protein supply worldwide (FAO, 1982). Generally, legumes contain 17-25% protein (about double that in most cereals) except  soybean  which contains  about  40% protein  (Enwere,  1998).  Legumes  are usually consumed in combination with cereals such as rice, maize, millet, and sorghum. They are sometimes combined with roots and tubers such as yam, cassava, potatoes, and cocoyam or consumed with plantains and bananas. Studies have shown that legume proteins complement cereal and roots to provide an ideal source of dietary protein of vegetable origin for human beings (Latham, 1997). This is because cereal protein which is deficient in lysine and rich in methionine and cystine  complement  legume proteins which are rich in lysine and poor in methionine and cystine (Bressani, 1975; Segal and Fawcelt, 1976).

Despite the high nutrient content of legume seeds, their utilization  is impaired  by some inherent constraints such as the presence of several antinutrients and food  toxicants. The type and concentration of these antinutrients vary in different legumes (Leiner, 1980). Lima bean has the highest content of hydrogen cyanide 10-312mg/100g) depending on the variety. The hydrogen cyanide content of other major legumes range  from 0.5mg/100g to

2.3mg/100g (Ologhobo et al; 1984).

It is obvious that plant foods contain a lot of antinutrients that affect availability and utilization    of   minerals.   Tannins,   phytates   and   food   toxicants    (anthocyanins    and haemagglutinin)  impart bitter and unacceptable taste to the  legumes.  They prevent protein digestibility  and decrease the absorption of divalent  metal ions in the intestine (Elegbede, 1998). Simple processing techniques can significantly reduce the levels of these antinutrients and  toxicants  in  plant  foods.  These  processing  techniques  include   soaking,  cooking, dehulling, germination (sprouting) and fermentation. Traditional method of processing plant foods lower the level of antinutrients and make nutrients much more available (Obizoba and Atii, 1994).

Despite the large number of existing grain legumes in Nigeria, their consumption as staple foods have centred mainly on cowpea and groundnut. Several other locally available species like the lima bean, pigeon pea and jack bean, which have remarkable adaptation to tropical conditions are less commonly used.

Lima bean is a lesser popular legume. This is because many communities  are  not aware  of  its  nutritional  potentials.  Lima  bean  could  easily  be  utilized  in  many  food preparations. It is usually consumed in combination with cereals such as rice, maize, sorghum or with roots and tubers such as yam, cocoyam, or with plantain. It is a good source of B- complex vitamins, protein, fibre, iron, zinc, potassium and magnesium (Apata and Ologhobo,

1994).

In developing countries, especially in Nigeria widespread food shortages, hunger and malnutrition have persisted, particularly among the low-income groups. In order to improve this situation, there is need for promotion of local food crops of high nutritional importance. The promotion of under exploited food crops with high nutritional potentials cannot be over- emphasized. This is because they make substantial contributions to the nutritional needs of the population, especially of the low-income groups.

1.2      STATEMENT OF  PROBLEM

Despite  the  efforts  to  combat  hunger  and  malnutrition  in  Nigeria,  they  are  still widespread  in  both  rural  and  urban  communities.  The  low-income  groups  suffer  most because they lack resources to procure, prepare and utilize adequate diets. Strict  economic measures,  inadequate  production,  processing  and  preservation  of  foods  militate  against provision  of protein  and micronutrient  rich foods.  Under-exploitation  and neglect  of our indigenous  food crops are some  of the  problems.  Lima  bean  is a lesser  known  legume, however,  it is a locally  available  food  crops which when adequately  processed  could be valuable tool to fight hunger and malnutrition.

1.3      OBJECTIVE OF THE STUDY

General objective: The thrust of this work was to identify the commonly consumed varieties  of  lima  bean  and  determine  the  effect  of  various  domestic  food  processing

techniques on the chemical, functional and sensory properties of their flours and blends with maize.

Specific objectives were to:

i.         identify the commonly consumed varieties of lima bean in Arondizuogu, Ideato

North L.G.A., Imo State, Nigeria;

ii.         determine the effects of food processing methods on the nutrients, antinutrients and food toxicants composition of lima bean and maize flours;

iii.        determine the functional properties of the flours;

iv.       select the flours (lima bean and maize) that had high nutrient profiles, formulate their composites and determine their nutrient composition;

v.        evaluate the organoleptic attributes of foods and snacks  based on the composite flours; and

vi.       prepare  and  assess  the  nutrient  content  of  two  traditional   dishes   (oshoto

and ikpaki) based on whole lima bean seeds and maize grains.

1.4      SIGNIFICANCE OF THE STUDY

The  results  of  this  study  would  increase  awareness  in  both  rural  and   urban communities  on  the  nutrient  potentials  of  lima  beans.  The  result  would  provide  basic information to food policy makers for justification for:

a.         instituting policies to promote this traditional food crop. b.        diversifying its use to improve food security.

c.         food industries  to use its flours  to produce  much cheaper  and nutritious  food substitutes.

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