Evaluation of maltogenic α-amylase and pre-gelatinized flour as anti-staling agents in scuffins

K. Birtle (1) and J. Purhagen (1,2)*
(1) Lund University, Department of Food Technology, Engineering and Nutrition, Lund, Sweden
(2) Perten Instruments AB, Garnisonsgatan 7a, 254 66 Helsingborg, Sweden
*Corresponding author: jpurhagen@perten.com

Abstract

A scuffin is a baked product similar to both a muffin and a scone. In this study scuffin recipes were developed including the two anti-staling substances maltogenic a-amylase (AMS) and pre-gelatinized rye whole meal flour (PgF,) to determine whether they had a reducing effect on staling. Amylopectin retrogradation and water redistribution and loss are believed to be significant causes of staling, which is the reason they are being measured in this study. In addition, volume, firmness and elasticity were measured in order to explain the aging process, and visual and sensory evaluations of the the samples were undertaken.  An increased amount of AMS and PgF did not always lead to better quality samples. The volume was decreased with the addition of AMS. Depending on the PgF concentration, the AMS had a different effect on the firmness. However, AMS was shown to not improve elasticity. Water migrated up from crumb to crust with storage, but no conclusions about how PgF affected the water migration could be drawn. A higher amount of PgF tended to reduce the amylopectin retrogradation.

Introduction

Staling, the aging of baked products excluding microbial spoilage is a major shelf-life limiting factor. It is a complex phenomenon which is not completely understood. The physical characteristics of staling include, among others, increased firmness, crumbliness, and whitening (Coultate, 2009, Knightly, 1977) Starch retrogradation, water redistribution and water loss are believed to be major causes of staling (Gray & Bemiller, 2003, Knightly, 1977).

In this study, scuffins were developed. A scuffin is a baked product with traits from both a scone and a muffin. The aim was to investigate how the two anti-staling substances, pre-gelatinized rye wholemeal flour (PgF) and maltogenic a-amylase (AMS), impacted the staling of the scuffins. Pre-gelatinized flour is cold swelling, i.e. more water can be added to the dough, compared to untreated counterpart, to get the same consistency. Thus, the moistness of the product may increase (Purhagen, 2011). Both pre-gelatinized flour and AMS have previously been shown to delay crumb firmness (Goesaert, et al., 2009, Hopek & Achremovicz, 2006).

Material and Methods

Strong wheat flour, fine rye flour, liquid sourdough, eggs, golden syrup, baking powder, salt, rapeseed oil, water, dried and sweetened cranberries, and vanilla extract. White poppy seeds were used as topping.  Commercial PgF was used, both as the sole anti-staling agent and in combination with an AMS.

Preparation of samples

TheThe dry ingredients were blended by hand and the wet ingredients were blended by a dough mixer, Varimixer Bjørn (A/S Wodschow & Co, Denmark), equipped with a flat beater. The liquid and the dry ingredients were then mixed together at minimum speed for 1 minute. Cranberries were added manually into muffin paper cups and the batter (40 (±1) g) was piped in afterwards. The resting time (while piping) was 20 minutes. The topping of 0.4+0.1 g of white poppy seeds was added. The scuffins were baked on a non-perforated baking sheet on the middle rack of an oven from Sveba Dahlen, Sweden, at 190°C for 14 minutes. After 5 minutes, the samples were covered with a towel and left to cool for 2 hours at room temperature. The scuffins were placed in a cardboard box and packed in an unperforated polyethylene bag. The samples were stored at room temperature and 50% humidity.

Volume measurements

A BVM-L450 from Perten Instruments, Sweden, with software version 3.4.3.64, firmware 2.00 and hardware 0.3, was used for volume measurements. Three scuffins from each recipe were measured each time. The instrument was calibrated according to the manufacturer’s recommendation before use.

Texture measurements

A TVT-300XP (Perten Instruments, Sweden), software TexCalc version 4.0.2.50 and 15 kg load cell, was used to measure firmness and elasticity of the crumb. A cylindrical probe with diameter of 36 mm was used. A hold-until-time measurement was performed. The sample high was 20 mm which was compressed by 30% with a holding time of 32 seconds. The test speed was 1 mm/s. Firmness was defined as the maximum peak force during the test. The elasticity was defined as the force measured after 30 seconds holding time divided by the maximum peak force. Three samples were measured. The instrument was calibrated according to the manufacturer’s recommendation before use. The crumb was defined according to figure 1.


Figure 1: Definition of crust, crumb and bottom crust.

Differential scanning calorimetry (DSC)

The enthalpy for melting amylopectin retrogradation was measured with a Seiko 6200 differential scanning calorimetry.  Between 8 and 10 mg samples were taken from the center of each scuffin. At day 2 after baking, one sample was taken from two scuffins, respectively. At day 4 and day 9, two samples from each scuffin were analyzed. An empty, coated aluminum sample pan was used as the reference. The scanning rate was 10°C/min from 8 to 140°C. After drying the sample in an oven for 24 hour at 105°C, the dry weight was measured. The dry weight was used for calculating the enthalpy of the amylopectin.

Water content measurements

The water content of crumb and crust was measured by Mettler Toledo, HB43-S Halogen moisture analyzer. Three samples of 2.0-2.5 g were measured from the recipes each time.

Visual evaluation and sensory analysis

Visually and sensory evaluations of the samples were undertaken at the same time as the measurements in terms of acceptability or unacceptability.

Experimental design

The experiments were divided into two parts. In the ingredients screening, part of the volume and texture were measured at days 1 and 7 after baking. Visual and sensory evaluation took place at the same time. The second part of the experiments was a shelf-life study.  Volume, texture and water content were measured on days 1, 3, 7 and 10 after baking. In addition, DSC and texture measurements were measured on days 2, 4 and 9 after baking.

Statistical analysis

Standard deviations and ANOVA single factor were used to analyze significant differences. If ANOVA showed a significant difference, a pair t-test assuming equal variances was performed. Grubbs’ test was used to determine outliers (Grubbs).

Results

Volume

At all PgF concentrations, the addition of 17 ppm AMS resulted in a significant decreased in volume of the product, figure 2. The different recipes are denoted with RX, where X=1, 2…18. Samples containing 5.3% PgF were significantly smaller, both with and without 17ppm AMS, compared to the lower PgF levels. The two AMS concentrations resulted in significantly different volumes at a PgF level of 0.2%, while this behavior was not found at a PgF level of 1.0%.


Figure 2: Volume of samples containing different PgF levels, with and without 17 ppm AMS.

Firmness

All samples became firmer with time. A combinational effect of AMS and PgF were found to have an impact on the firmness. The AMS had either no, improved or adverse effect of the firmness after one week of storage at PgF level of 0.2%, 1.0%, and 5.3%, respectively. In figure 3 it can be seen that the addition of AMS to a PgF level of 5.3% resulted in firmer results. However, there was no significant difference in firmness between the two AMS level 17 ppm and 34 ppm after one week of storage for the tested PgF levels.


Figure 3: Firmness as function of storage day for samples containing 5.3% PgF.

Elasticity

During storage the samples became less elastic. Independent of the PgF concentration, the AMS did not have any significant impact on elasticity after one week of storage. However, when comparing the PgF levels to each other at the AMS level of 17 ppm, the samples containing 5.3% PgF were the majority of the days significantly more elastic than the lower PgF levels on most of the days (Figure 4).

Water content

Water migrated from crumb to crust and water loss occurred during storage. PgF or AMS levels did not make a significant difference to water content.

Amylopectin retrogradation

Samples containing 5.3% PgF tended to contain less retrograded amylopectin compared to 0.2% and 1.0% PgF, figure 5. However, the result was not significant.

Figure 4: Elasticity as function of storage day for samples containing different PgF levels and a constant AMS level.

Figure 5: Enthalpy (ΔH) as a function of storage days.

Visual appearance and sensory analysis

The samples containing 5.3% PgF, independent of AMS concentration and storage days, were regarded as unacceptable. All other samples were considered acceptable both visually and sensually at day 10, but all samples were microbial spoiled at day 15.

Discussion

Volume

An explanation as to why the addition of AMS generated smaller samples is that it might have weakened the three-dimensional structure of the starch. Thus, the gas holding capacity was impaired and the volume of the samples became smaller. PgF is more accessible to enzymatic hydrolysis compared to normal flour partly due to its pre-treatment (Hopek & Achremovicz, 2006). This might explain why samples containing 5.3% were significantly smaller. It tended to not be an effect of the AMS on PgF level of 0.2%, which was shown in firmness results. Therefore, the differences in volume between the two AMS concentrations were likely to depend on the individual samples were measured.

Firmness

In this study it was shown that the firmness was positively correlated to a smaller volume. The samples that contained 5.3% PgF and 17 ppm AMS were firmest and also smallest, figure 6. This is likely due to the enzymatic hydrolysis. With a weakened three-dimensional structure of starch the texture becomes compact and firm. It was unexpected that samples containing 34 ppm AMS was not significantly softer than 17 ppm. If the flour had a higher percentage of the ingredients, the starch would have had more influence on the texture. This might have shown another result of the difference in concentrations of AMS compared to this study.


Figure 6: Volume as function of firmness.

Elasticity

As expected, the elasticity decreased during storage. Water that functions as a plasticizer was redistributed within the sample during storage and can be one explanation for decreased elasticity. Less structural changes tended to occur at a PgF level of 5.3% compared to the lower levels. This was partly confirmed by the retrogradation enthalpy of the DSC measurements.

Amylopectin retrogradation

Starch in PgF is more accessible to enzymatic hydrolysis than normal wheat flour (Hopek & Achremovicz, 2006). Therefore, it is likely that there was no significant difference in retrogradation enthalpy between 5.3% PgF and the lower concentrations, due to error in measurements and the individual samples were measured.

Conclusions

In this study, microbial spoilage and not staling were limiting the shelf-life for samples containing 0.2% and 1.0% PgF. The samples containing 5.3% were already sensorial and visually evaluated as unacceptable when newly baked. Also measurements showed that an increase in the two anti-staling substances did not necessarily lead to properties related to better quality. Addition of AMS generally leads to smaller samples. When 5.3% PgF was added it resulted in the smallest volumes. All samples became firmer with time and a combination of the anti-staling substances affected firmness. The AMS had no, an improved and an impaired effect on firmness respectively, when 0.2%, 1.0% and 5.3% PgF was used. The elasticity decreased with time for all samples and AMS did not have any improving effect on elasticity. No significant differences were found in amylopectin retrogradation, but the use of 5.3% PgF tended to reduce the amount of retrograded starch. Water migrated from crumb to crust during storage, but there were no conclusions on how the different levels of PgF affected the water retention.

References

Coultate, T. P. (2009). Food: The Chemistry of its Components. Cambridge: Royal Society of Chemistry.

Goesaert, H., Slade, L., Levine, H., & Delcour, J. A. (2009). Amylases and Bread Firming - An Integrated View. Journal of Cereal Science, 50:(345-352).

Gray, J. A., & Bemiller, J. N. (2003). Bread Staling: Molecular Basis and Control. Food Science and Food Safety, 2:(1-21).

Grubbs, http://graphpad.com/quickcalcs/grubbs1/ , 21 April 2016

Hopek, M. Z. R., & Achremovicz, B. (2006). Comparison of the Effects of Microbial Alfa-Amylases and Scalded Flour on Bread Quality. Acta Sci. Pol., Technol. Aliment., 5:(97-106).

Knightly, W. (1977). The Staling of Bread. The Bakers Digest:(51-52).

Purhagen, J. K. (2011). Staling and Starch Retrogradation in Speciality Bread. Lund University, Lund.