Introduction

Oxidising agents have a beneficial effect on dough properties and attributes including volume, texture and crumb structure of baked products (Van Oort et al 1997). Replacement of chemical oxidizers by enzymatic ones (for example, peroxidase (POX) EC 1.11.1.7) could have the benefit of more specific and better controlled oxidation processes. It is proposed that although the making of bread and noodles have little in commen, the action of POX might be useful to improve the textural properties of Asian noodle products, furthermore, the application of such an enzyme might eliminate the use of other synthetic ingredients. In addition, this enzyme seems to be crucial for colour quality as it effectively bleaches carotene. Hsieh and McDonald observed that a purified lipoxygenase from durum wheat endosperm also showed POX activity (Hsieh and McDonald, 1984). This indicates a direct link of POX to colour properties of wheat end products. It seems to decrease the yellow colour intensity of flour, probably by decreasing lutein content due to oxidation. This might be of significance for WSN noodles as clear white colour is preferred for this product. Thus, the main objective of this study has been to evaluate the effect of POX addition to the WSN formulation. Quality attributes evaluated included texture, colour, structure and cooking quality.

Materials and methods

Ultra White (UW) and P-Farina (PF) flours - (Goodman Fielder – Melbourne) were used for the preparation of WSN. All chemicals and enzyme preparations were obtained from Sigma–Aldrich and Biomedicals Inc. The activity of peroxidase (from horseradish) was assayed by a method modified from those of Delcros et al 1998 and Iori et al 1995. Two preparations of POX both from horseradish were tried (liquid preparation from Sigma–Aldrich; powder preparation from MP Biomedicals). The liquid preparation of POX was added directly to the noodle formulation during the water addition stage of the processing. The freeze-dried powder preparations of POX were dissolved in distilled water prior to addition to the noodle formulation. The final level of POX addition was 72.0 × 10³U/batch of noodles (POX from Biomedicals was used to complete the study; one KU of POX will form 1mg purpurogallin in 20 seconds from pyrogallol at pH 6.0 and 20°C). A series of different additions were tried. Textural properties of noodles were measured using the Texture Analyser (TA-XT2) using two different attachments a cylinder probe (P/45) and a blade. Noodle colour was measured using a Minolta Chroma Meter (CR300) (RACI 1995). Structural properties of noodle surface were studied using the environmental scanning microscope (ESEM) for raw noodle sheets while cooked noodles were freeze-dried first and then viewed using the scanning electron microscope (SEM). The formulation and processing of WSN followed the method of Moss et al 1987. Sub-samples were stored fresh in polyethylene bags at room temperature (~ 25°C) and refrigeration temperatures (4°C) as well as in the dried form. Noodle drying was for 30hr at 40°C in a convection oven.

Results and discussion

Relatively high levels of POX were found in the flours studied and some losses in the original activity have been observed during processing, but then relative stability of the enzyme has been obtained during the storage of noodles under various conditions (Table 1).

Table 1. Levels of POX in control WSN and supplemented with Biomedicals POX

POX from Sigma-Aldrich

The effect of two different levels of addition of POX to the noodle formulation is shown in Fig 1. The textural differences were recorded using the cylinder probe (P/45) as noodle hardness and the flat blade as noodle firmness In both cases no significant differences were seen among the treatments, although the dough was tougher to handle as compared to the control samples.

POX from MP Biomedicals

Textural profile of WSN is shown in Figure 2 and these graphs indicate the reverse of those found when Sigma Aldrich preparations were used. Lower amounts of addition seem to result in softer noodles when hardness was measured; as the addition of POX increased so did the hardness values. The same was found for both raw and cooked noodle preparations. When the same preparations were used and noodle firmness (relating to the bite action) was measured (blade method) the lower amount of POX addition seemed to give slightly firmer noodles and the highest level of addition used resulted in less firmer noodles. Both of these measurements although measuring different properties can be useful in trying to understand the complicated meaning of noodle chewiness.

Colour

Discolouration of noodle sheets was studied using the POX preparation from MP Biomedicals (the level of addition was 72.0 × 10³U per batch of noodles). Addition of POX resulted in undesirable darker yellow to brown colour of WSN. Figure 3 show colour properties of dried and dried and cooked noodles (made from both flours UW and PF treated with POX). Discolouration of noodle sheets is more obvious in dried noodles, while the difference in colour as measured with the Minolta was not as obvious once noodles had been cooked. Darkening of noodle sheets occurred in all samples (control included) but was even more prominent upon POX addition. Discolouration was faster and it occurred earlier in noodles stored at 25°C as compared to noodles stored at 4°C (results not shown here).

Figure. 1 The impact of Sigma POX on textural properties of WSN made from UW flour: Fresh raw (top left) and fresh cooked (top right) measured using the P/45 flat cylinder probe WSN. Raw (left) and cooked (right) lower measured with the blade attachment. 1 unit forms 1.0mg purpurogallin from pyrogallol in 20 seconds at pH 6.0 and 20°C. Error bars represent standard deviation values.

Figure. 2 The impact of Biomedicals POX on textural properties of WSN made from UW flour: Fresh raw (top left) and fresh cooked (top right) measured using the P/45 flat cylinder probe WSN. Raw (left) and cooked (right) lower measured with the blade attachment. 1 unit forms 1.0mg purpurogallin from pyrogallol in 20 seconds at pH 6.0 and 20°C. Error bars represent standard deviation values.

Figure. 3 Colour properties of WSN: L* whiteness values (upper) and b* yellowness (lower) for dried (left) and dried and cooked (right). UW, Ultra white, PF, P-Farina; POX, peroxidase (MP Biomedicals; 72.0×10³U/batch). Error bars represent standard deviation values.

Conclusions

Discoloration of noodle sheets occurred at both storage temperatures, but was more obvious and it occurred earlier in noodles stored at 25°C as compared to noodles stored at 4°C for a total period of 96 h. Upon the addition of POX darker noodles were seen following drying consistent with higher enzyme activity at elevated temperatures. The addition of POX significantly increased the darkening of noodle sheets thus making enzyme addition undesirable in the manufacture of WSN. Textural properties of WSN showed little variation after storage at the two different temperatures. However, in some cases noodles stored at 4°C appeared to be slightly firmer. Higher additions of POX resulted in slightly firmer noodles. At lower levels the enzyme preparations might have been manipulated within the noodle formulation to obtain good quality soft products, if it was not for its highly undesirable effect upon the colour of these types of noodles.

References

Delcros, J-F., Rakotozafy, L., Boussard, A., Davidou, S., Porte, C., Potus, J., and Nicholas, J. (1998). Cereal Chem. 75: 85-93.

Hsieh, C. C., and McDonald, C. E. (1984). Cereal Chem. 61: 392-398.

Iori, R., Cavalieri, B. and Palmieri S. (1995). Cereal Chem. 72:176-181.

Moss, R., Gore, P. J., and Murray, I. C. (1987). Food Microstructure. 6: 63-74.

RACI 1995 Official Testing Methods. RACI Cereal Chemistry Division, Melbourne.

Van Oort, M., Hennik, H., and Moonene, H. (1997). In The first European symposium on enzymes and grain processing. Ed. Angelino, S., Hamer, R., Van Hartingsveldt, W., Heidekamp, F., Van Der Lugt, J. P. Published by TNO Nutrition & Food Research Institute – Zeist, The Netherlands. Pp 195-205.