Cereal Phytase

download Cereal Phytase

of 23

  • date post

    06-Apr-2018
  • Category

    Documents

  • view

    219
  • download

    0

Embed Size (px)

Transcript of Cereal Phytase

  • 8/3/2019 Cereal Phytase

    1/23

    1

    Effect of germination on the phytase activity, phytate and total phosphorus contents of

    some Nigerian grown cereals

    Marshall A. Azeke*, Samuel J. Egielewa, Mary U. Eigbogbo, Godwin I. Ihimire

    Department of Biochemistry,

    Ambrose Alli University,

    P. M. B. 14

    Ekpoma, Nigeria

    *Corresponding Author, Tel: +234 805 6174857; Fax: +234 1 2637021,

    E-mail: [email protected]

  • 8/3/2019 Cereal Phytase

    2/23

    2

    Abstract

    The level of phytase activity, phytate and phosphorus contents of five Nigeria grown cereal

    grains were determined. The cereals screened were rice (Oriza sativa), maize ( Zea mays),

    millet (Panicum miliaceum), sorghum (Sorghum bicolor) and wheat (Triticum aestivum). The

    cereal grains were also germination for 10 days in order to assess the responses of the

    aforementioned parameters. Phytase activities were generally high (0.21 0.67 U g-1) in all

    samples. Phytate content ranged between 5.58 and 6.23 g/kg-1

    while total phosphorus content

    ranged between 3.33 and 4.34 g/kg-1

    . The level of phytase activity reached its maximal value

    after seven (16-fold), six (5-fold), five (7-fold), seven (3-fold) and eight (6-fold) days of

    germination for rice, maize, millet, sorghum and wheat respectively. Following this initial

    period, phytase activity declined slightly (P < 0.05). The increase in phytase activity during

    germination was accompanied by a significant reduction in phytate (P < 0.05) and a small but

    significant increase in total phosphorus. The increase in phytase activity and the

    accompanying decrease in phytate content could have positive implication for the nutrition of

    poultry and ruminants and for the environment.

    Keywords: Cereal, phytase, phytate, phosphorus, germination.

  • 8/3/2019 Cereal Phytase

    3/23

    3

    INTRODUCTION

    Cereals and legumes form a significant portion of the food supply for humans and other

    animals, as they are a major source of carbohydrates, proteins, lipids and minerals (Katina et

    al., 2005). The presence of antinutrients such as phytate has been a major limiting factor to

    the extensive utilization of these plant resources (Al-Numair et al., 2009). Phytate, myo-

    inositol (1,2,3,4,5,6) hexakisphosphate, is present in high concentrations in many food items

    derived from plants. It is the major storage form of phosphorus in mature grains and legumes

    (Kumar et al., 2010). Its hydrolysis is catalysed by the enzyme phytase (myoinositol

    hexaphosphate phosphohydrolase) to inositol and orthophosphate. About 60

    90 % of total

    phosphorus in plant feedstuffs is bound as phytate phosphorus (Loewus, 2002). Phosphorus,

    in this form, is not utilised by human beings, birds or agastric animals because they lack the

    sufficient endogenous intestinal digestive enzyme phytase which releases orthophosphate

    from the phytate molecule in the gastrointestinal tract (Holm et al., 2002). The unabsorbed

    phytate is excreted and contributes to phosphate pollution in water bodies downstream of

    agriculturally intensive areas (Sharpley, 1999). Furthermore, phytate works in a broad pH-

    region as a highly negatively charged ion and therefore its presence in the diet has a negative

    impact on the bioavailability of divalent and trivalent mineral ions such as Zn2+, Fe2+/3+, Ca2+,

    Mg2+

    , Mn2+

    and Cu2+

    (Fredlund et al., 2006; Lopez et al., 2002; Lnnerdal, 2002). The need

    to maintain sufficient dietary phosphorus levels while reducing phosphorus excretion in

    poultry manure has led to an increase in the application of phytase to poultry feed (Hatten et

    al., 2001). The phytases (myo-inositol hexakisphosphate phosphohydrolases) are a subfamily

    of the high-molecular-weight histidine acid phosphatases. They catalyse the phosphate

    monoester hydrolysis of phytate,which results in the stepwise formation of myo-inositol

    pentakis-,tetrakis-, tris-, bis-, and monophosphates, as well as the liberation

    of inorganic

    phosphate (Sathe and Reddy, 2002). The use of phytase reduces phosphorus excretion in

  • 8/3/2019 Cereal Phytase

    4/23

    4

    poultry manure by allowing the birds to utilize more of the phytate phosphorus (Sharpley,

    1999). The use of phytase may also free cations and proteases bound in phytate phosphorus

    complexes and improve many production parameters and body structure characteristics in

    broilers and laying hens, such as body weight, bone ash content, feed consumption, egg

    weight, and egg shell quality (Zyla et al., 1999; Hatten et al., 2001). The phytases used for

    this purpose are usually of microbial origin and the technology involved in the extraction,

    purification and thermo-stabilization of the enzymes is still beyond the reach of developing

    countries especially in Africa. High native phytase activities are present in cereals and cereal

    by-products, whereas lower activities have been reported for legume seeds (Viveros et al.,

    2000; Zimmermann et al., 2002; Steiner et al., 2007). However, no studies have been carried

    out on the distribution of phytase activity in cereals grown in Nigeria. The current study was

    conducted to assess phytase activities and the contents of phytate and total phosphorus in

    samples of different Nigerian grown cereal grains as influenced by sprouting.

    MATERIALS AND METHODS

    Samples

    Seed samples harvested in 2008 were purchased from local farmers in Edo State in Mid-

    Western Nigeria. The legumes screened are: rice (Oriza sativa), maize ( Zea mays), millet

    (Panicum miliaceum), sorghum (Sorghum bicolor) and wheat (Triticum aestivum).

    Surface Sterilization and Germination of seeds

    For surface sterilization, seeds were soaked in 0.5% NaOCl for 3 minutes, rinsed very well

    with some quantity of sterile water and soaked again in of 0.75% H2O2 for 2 minutes and

    again rinsed thoroughly with sterile water. After draining, the grains were spread on plastic

    trays overlaid with wet tissue papers. The seeds were then allowed to germinate in disinfected

  • 8/3/2019 Cereal Phytase

    5/23

    5

    dark cupboards for 0 10 days with daily harvestings. The seeds were rinsed once a day with

    sterile water, which was removed completely. For the determination of Phytate and total

    phosphorus, the harvested samples were oven dried at 60 C for about 18 h, allowed to cool

    and then milled. Freshly harvested samples were used for phytase activity determination.

    Portions of freshly harvested and the dried, milled samples were used for moisture

    determination.

    Enzyme preparation

    The preparation of the crude enzyme was basically as described by Senna et al. (2006). Fresh

    samples of ungerminated and germinated seeds were homogenized in 0.1 M sodium acetate

    buffer (pH 5.0). The homogenate was centrifuged at 12,000 g for 5 min. The pellets were

    discarded and supernatants were used for enzyme assays, described as total homogenate. All

    procedures were carried out at 4 C.

    Enzyme activity

    Enzyme activity was determined at 40 C. The assay mixture consisted of 350 L of 0.1 M

    sodium acetate buffer, pH 5.0 and 100 L of 2 mM sodium phytate. This mixture was pre-

    incubated for 10 min at 40C and the enzymatic reactions were started by adding 100 L of

    the crude enzyme to the pre-incubated assay mixtures. After incubation at 40 C for 30 min,

    the liberated phosphate was measured by using the ammonium molybdate method (Heinonen

    and Lahti, 1981). Added to the assay mixture were 1.5 mL of a freshly prepared solution of

    acetone/5 N H2SO4/10 mM ammonium molybdate (2:1:1 v/v) and 100 L of 1.0 M citric acid.

    Any cloudiness was removed by centrifugation prior to measurement of the absorbance at 355

    nm. To calculate the enzyme activity, a calibration curve was produced over the range of 5-

    600 nmol of phosphate ( = 8.7 cm2

    mol-1

    ). Activity (units) was expressed as 1 mol of

  • 8/3/2019 Cereal Phytase

    6/23

    6

    phosphate liberated per minute. Blanks were run by adding the ammonium molybdate

    solution prior to adding the enzyme to the assay mixture.

    Phytate Extraction and Determination

    Phytate extraction and determination was essentially according to the method of Wheeler and

    Ferrel (1971) with slight modifications. Instead of extraction using 3 % TCA, 1.2 M HCl

    containing 10 % Na2SO4 was used because of excessive foaming with TCA (Azeke et al.,

    2005).

    Total Phosphorus Determination

    The method of Jacobs (1999) was applied for the determination of total phosphorus. This

    involved digestion of seeds (5 g) with 30 ml conc. HNO3 and 20 ml conc. H2SO4.

    Statistics

    Significance of difference was tested by analysis of variance and Tukey-Kramer test using the

    GraphPad InStat version 2.04a (GraphPad Software Inc, San Diego, California, USA,

    www.graphpad.com)

    RESULTS AND DISCUSSION

    Distribution of phytase activity, phytate and total phosphorus in cereal grains

    The phytase activities, phytate and total phosphorus contents of some Nigerian grown cereal

    grains are shown in table 1. With the exception of maize and sorghum significant differences

    (P < 0.05) were observed in the phytase activities (0.21 0.67 U g-1) of the cereal grains

    screened. Steiner et al. (2007) reported a range of 0.4 6.0 U g-1

    for oats, barley, triticale, rye

    and wheat. They reported 2.8 U g-1