EFFECT OF EXTRUSION COOKING ON THE PROPERTIES AND ACCEPTABILITY OF BREAD-CRUMB-LIKE COATING PRODUCTS

ABSTRACT

Bread crumb-like products are often used in the food industry to enhance fried-like texture. These have been made by the traditional method of crumb production. In the present work, an attempt has been made to produce superbake breadcrumb by extrusion on a BC-45. Extruded products were evaluated for density, expansion, fat uptake and taste. The results obtained showed that extrusion conditions singly or in combination affected the properties of the breadcrumb. High temperature and low moisture content gave less dense product, which affected frying behavior of chicken cubes. Oil absorption was reduced slightly with increased extrusion temperature. An acceptability test of two extruded breadcrumbs against Morton's a commercial product used as control, was determined in application on chicken nuggets. A significant difference was found between the acceptability of the Morton's breadcrumbs and one of the samples (Tech 42810) extruded at 120°C.

INTRODUCTION

Coatings are typically used in the food industry to form a seal against moisture loss during frozen storage and consumer reheating. During reheating, coatings can absorb the natural juices of a food product while maintaining a desirable, crispy outer surface and thereby conserving and retaining the natural flavour and nutritive value of the food.

Consumers typically enjoyed food with a fried-like taste and texture. However, consumers also typically prefer the ease and simplicity as well as the low fat absorption of baking or cooking as an alternative to frying. Consequently, the food industry has responded by developing products, which upon conventional oven reheating result in food with a fried-like texture and flavour. Bread crumb-like products are often used in the food industry to enhance fried-like texture of foods.[1]

The traditional method for the production of breadcrumb comprises production of dough, short fermentation, and baking, followed by pre-crushing drying, milling, sieving to the required particle size distribution, and packaging. Using the conventional yeast leavening procedure, the time required for improvements in the bread firmness and crumbliness otherwise referred to as staling is normally about 1 to 3 days, necessitating a large space for storage while staling occurs.[2] Because of the time required and the number of steps needed to make conventional breadcrumb, several attempts were made to streamline the process to make it less time consuming and more economical.

The use of gaseous materials such as carbon dioxide for leavening of bread has been reported.[3] Extrusion cooking has become a well-established industrial process, which offers the possibility of producing a wide range of breadcrumb products based on different recipes.[4] Musao Seki[5] has demonstrated the production of breadcrumb by extrusion from an essentially yeast free mixture obtained by adding 0.5–6.0% soybean protein to wheat flour and mixing with salt, fats, emulsifier, pH adjuster, colouring material, flavouring material and alpha-converted starch and then extruding from a die in a rope-like configuration. The rope-like material is drawn from the die of the extruder at a speed greater than the extrusion speed to produce bubbles in the rope-like material. The material is then flattened, cut and crushed, and dried. This method was reported to produces a bread crumb-like product within 8 h compared to the conventional process which takes up to 36 h.

A cost effective superbake breadcrumb produced by conventional methods has been developed by the Morton's company (UK) for the chilled and frozen markets. This superbake breadcrumb has the characteristics of crisp but melt-in-the-mouth texture, good sink ratio which prevents carbonization and unacceptable appearance of fried food material and minimal fat uptake which controls the amount of fatty material ingested by the consumer and also limits the cost of manufacture. There are no reports on the use of extrusion for production of superbake breadcrumb. The objective of this study was to evaluate the properties and acceptability of superbake breadcrumb produced by extrusion outlined in this work.

MATERIALS AND METHOD

Materials

Wheat flour and defatted soy flour, baking powder, pregelled starch (Atlantis 3000), sugar, salt and glycerol were purchased from the local market. Emulsifier (Monogleceryl fatty acid ester) was purchased from Danisco Co LTD. All the ingredients were mixed with an 18.9-L Hobart Mixer (Model A200F, Hobart Corp., USA) for 20 min.

Method

The extruder used in this project was a Clextral X-5 model BC 45 co-rotating twin screw equipped with two barrel sections. The screws were 5.55 cm in diameter and had an overall active length of 50 cm. The extruder was operated at 150 and 155 rpm. A 14.7 KW DC motor was used to drive the extruder. Moisture content of the feed was controlled at 27 and 30% by injecting water into the extruder with a pump. An adjustable cutter with four blades facing the die was operated at 300 rpm to cut the extrudate as it emerges from the extruder. Extruder temperatures measured by a PC computer were 100 and 120°C for the two extruded samples respectively. Glycerol solution (20%) was injected into the barrel during extrusion in some cases. The extrudates (pellet) were dried in a steam heated Tek-Dryer equipped with an exhaust fan at 100°C for 35 min.

Analytical Procedure

Moisture

Moisture content of samples was determined based on the standard AOAC method 925.10.[6]

Bulk Density

Bulk density determination using glass beads was carried out as outlined by Hwang and Hayakawa.[7] The cylinder with glass beads and pieces of extrudate was weighed and the bulk density (ρ _b ) calculated.

where W _ex =weight of extrudate; W _gbd =weight of glass beads; and ρ _gb =bulk density of glass beads.

Expansion Ratio

Expansion of extrudate was expressed as the ratio of the cross sectional area of the rod shaped extrudate over the cross sectional area of the diameter of the die and was measured as described by Colonna et al.[8] Averages of ten readings were taken.

Fat Uptake

Sample (10 g) was weighed and placed in a clear sieve (mesh size 1.4–2.0 mm). The sieve was then lowered into melted animal fat heated to 190°C for two minutes with agitation after one minute. After 1.5 min of frying the approximate percentage of the sample, which had sunk to the base of the sieve, was noted to determine the sink/float ratio. At exactly 2 min, the sample in the sieve was raised from the hot fat and allowed to drain for 1 min with agitation at 30 sec interval.

The fried sample was placed onto an absorbent paper and allowed to cool for 5 min and the weighed along with the paper (A). After weighing, the crumb was removed and the paper weighed alone (B). The procedure was repeated five times and the initial weight (10 g) of the sample was subtracted from the difference between A and B to give the value of fat taken up by the sample {(A−B)−10} in mg/g.

Product Acceptability Test

The product acceptability test was conducted to determine the acceptability of the extruded breadcrumb samples against a market leader (Morton Foods'), which served as control. The three breadcrumbs were: Morton's, Tech Center 42810 extruded at 120°C and Tech Center 30111 extruded at 100°C.

Preparation of Samples

Pregelled wheat flour (ABR Goldfield 0020w, 70%), maize flour (25%) and wheat flour (5%) were mixed with water at a ratio of 1:1 to make a batter. Approximately even sized pieces of chicken (Asda chicken breast fillet) were dipped in the batter for about 5 sec. The excess batter was shaken off, and the nugget lightly pressed into the crumb to give a total weight of about 20–25 g per nugget. The nuggets were then fried for one minute, at 190°C, in fresh vegetable oil in the Lincat double fryer. The nuggets were then frozen for four days. They were heated in the Hobart oven at 200°C for twenty minutes and turned once over after ten minutes. The position of the samples in the oven was rotated between batches in order to minimize oven temperature variations. The samples were served at 85–90°C.

Sensory Method and Data Analysis

Thirty-eight panelists from within and outside the British Sugar Technical Center were recruited for the test. Each taster was presented with one each of the three nuggets on coded paper plates with plastic knifes and forks. The serving order was balanced and randomized over panelists. The panelists were told to concentrate on the coating rather than the chicken. They were also asked about their frequency of consumption of breaded fish and chicken (more/less than once a month) and to explain what they particularly liked or disliked about each coating. Each breadcrumb was scored for taste from 1 (extremely dislike) to 9 (extremely like). An analysis of variance was performed on the acceptability scores to determine if a statistically significant difference existed. The Least Significant Difference was calculated to determine the relationship among the three breadcrumbs.

RESULTS AND DISCUSSION

Extrusion Effect on the Physical Properties

Analysis of variance showed that moisture, temperature of extruder had a significant effect on expansion ratio and bulk density, which controls the sink float properties of extruded breadcrumb. Increasing the temperature resulted in the decrease in the extrudate bulk density (27.4 g/100 ml) compared to that of lower temperature (29.2 g/100 mL) (Table 4). Liu et al.[9] made similar observations (2000). Fat uptake decreased slightly with increase in temperature (Table 2) compared to sample extruded at lower temperature. This observation is similar to the finding of Alfonso et al.[10]

Table 1. General Formulations of Extruded Breadcrumb

Formulations	Wheat Flour	Defatted Soy Flour	Salt	Emulsifier*	Fat	Baking Powder**	Pregelled Starch	Sugar	Glycl.
F1	81.5	2.5	2	0.3		2.8	7.5	3.4	0
F2#	74	5	2	0.3		2.8	7.5	3.4	5
F3	79	5	2	0.3		2.8	7.5	3.4	0
F4	81.5	5	2	0.3		2.8	0	3.4	5
F5	84	2.5	2	0.3		2.8	0	3.4	5
F6	86.5	5	2	0.3		2.8	0	3.4	0
F7	76.5	2.5	2	0.3		2.8	7.5	3.4	5
F8	89	2.5	2	0.3		2.8	0	3.4	0
F9	84	5	2	0.3		2.8	0	3.4	2.5
F10	77	5	2	0.3	2	2.8	7.5	3.4	0
F11	79	5	2	0.3		2.8	7.5	3.4	0
F12	79.8	5	2	0.3		2	0	3.4	0
F13	77.8	5	2	0.3		4	0	3.4	5
F15	88.7	5	2	0.3		4	0	0	0
F16	90.7	5	2	0.3		2	0	0	0
F17	89.7	5	2	0.3	1	2	0	0	0

*Monoglyceyl fatty acid ester.

**Mixtures of Disodium hydrogen phosphate, sodium bicarbonate and wheat flour.

#Basic formulation of superbake breadcrumb.

Table 2. Characteristics of Tasted Samples

Sample	Control (Morton's)	Tech. 42810	Tech. 30111
Formulation		F15	F15
Screw speed (rpm)		150	140
Barrel moisture (%)		27	30
Barrel temperature (°C)		120	100
Flow rate (Kg/hr)		61	55
Moisture of final particle (%)	8	3.89	2.5
Bulk density (g/100 mL)	24	27.4	29.2
Sink ratio (%)	95	95	90
Fat uptake (mg/g)	0.48	0.44	0.52

Table 3. Effect of Glycerol, Pregelled Starch, and Soya Flour on the Texture of Extruded Breadcrumb

Formula	Des. No.	Run No.	Glycerol (%)	Pre.starch (%)	Soy Flour (%)	Texture Score
F8	1	8	0	0	2.5	7
F5	2	5	5	0	2.5	9
F1	3	1	0	7.5	2.5	6
F7	4	7	5	7.5	2.5	6.5
F6	5	6	0	0	5	7.5
F5	6	5	5	0	5	8.5
F3	7	3	0	7.5	5	8.5
F2	8	2	5	7.5	5	7.5
Average Score	Glycerol		Pre. Starch		Soya Flour
Low level	7.25		8.00		7.13
High level	7.88		7.13		8.00
Difference	0.63		0.87		0.87
Difference per 2.5% change	0.315		0.29		0.87

Table 4. Comparison of Bulk Density in Different Barrel Temperature Groups

Barrel Temperature	Groups	Count	Sum	Bulk Density	Variance
120°C	Column 1	21	575.4	27.4	7.434
100°C	Column 2	19	525.7	29.2	11.477
Source of Variance
	SS	Df	MS	F	P-value	F-crit
Between group	31.59722	1	31.59722	3.40062	0.073191	4.10546
Within group	343.7894	37	9.291607
Total	375.3867	38

Barrel moisture is a key factor in extrudate characteristics.[11] With the decrease of moisture content, the material flow within the extruder may be restricted thus increasing the residence time, shear rate, torque and the die temperature respectively, this consumed more energy and set up a high pressure which gave the extrudate lower density. Good scores in taste test are usually from those with lower density.

Screw speed had a significant effect on bulk density of extrudate at 150 rpm. At higher screw speed, the residence time became shorter thus giving product with less functionality. The extruder was run at two separate feed rates of 55 and 61 kg/hr. At higher flow rate, a higher pressure was built up behind the die because higher energy was consumed by friction. Also, the higher feed rate affected the residence time in the extruder. This made a significant difference (P<0.01) in die pressure between two different flow rate groups. Even though there was a very significant change in die pressure with different flow rates, there was no significant difference in bulk density between the two flow rate groups, although the bulk density in higher flow rate group (28.04 g/100 mL) is lower than that in lower flow rate group (28.35 g/100 mL).

Extrusion Effect on Texture of Extruded Breadcrumb

Increased screw speed resulted in increased expansion of the extruded product as a result of increase in product temperature.[9] This led to a drop in the hardness but contributed to the crispness of the breadcrumb. Increase or decrease in moisture content affected the bulk density of the extrudate, which had an overall effect on taste, and texture of the breadcrumb (Fig. 1). Increasing the moisture content above 27% resulted in a dense breadcrumb, which affected frying procedure. Moisture loss was rapid during frying leading to replacement of water by fat in the fried product thus giving a product that was too oily to touch and taste. The low moisture content on the other hand, gave a much lower density, which caused the extrudate to float during frying thus giving a white spot on the fried sample (frosting). Increase in temperature resulted in low fat uptake (Table 2), probably due to decrease in the number of hydrophobic sites in the added soy protein brought about by the high temperature of extrusion.[10]

Figure 1. Effect of moisture content on bulk density.

Effect of Level of Ingredients on Extrudate Texture

The effect of addition of ingredient on product characteristics is given in Table 3. The addition of soy flour had more impact on the texture of the extrudate than the addition of glycerol and pregelled starch. High level of soy flour (5%) gave a better texture. Guska and Khan,[12] have reported that increase in temperature of extrusion can impart a good texture to a product as a result of the modification of starch and protein components under high temperature. Similarly, Lahl et al.[13] reported that hydrolysis of food protein during heat treatment can impart good texture to food. The addition of glycerol made an insignificant contribution to the texture of the extruded breadcrumb probably due to the surfactant properties of glycerol, which limited expansion and thus did not enhance texture.

Two different addition levels of baking powder in the formulation (2% and 4%) were compared in a designed experiment with different barrel moisture contents as shown in Fig. 2. At lower moisture level (25%), the effect of baking powder was insignificant due to less expansion in a limited water system and hence a low bulk density crumb. But as moisture content was increased to 27%, there was some expansion, however, the contracting effect of the baking powder still dominated. At higher moisture content above 27%, probably due to dilution effect, increase in the volume of the breadcrumb dominated the contracting effect of the baking powder resulting in a dense breadcrumb. There was a significant change in bulk density between the different addition levels of baking powder. High level of baking powder gave lower bulk density associated with better texture in taste because above 2% inclusion level, the contracting effect of the baking powder was more significant. From the results, it appears that reducing the baking powder level increased the density making the crumbs too dense.

Figure 2. Effect of baking powder level on the bulk density of extruded breadcrumb.

Taste Acceptability

When the data were examined, approximately half the tasters were frequent consumers of breaded products. And thus, the data were therefore additionally split into two groups identified as frequent consumers and total consumers and an analysis of variance was performed on the separate groups. No significant difference was found between the acceptability of the samples at the 90% confidence level when all tasters were included. However, when only the data for the total consumers were included a statistically significant difference (P<0.1) was apparent. When the extruded samples are statistically compared to the Morton's sample, there is a very significant difference (P<0.01) between every extruded sample and the Morton's even when all the tasters were included (Fig. 3). There was no significant difference between the two extruded samples whether the statistics were from the frequent consumers or total consumers.

Figure 3. Acceptability of breadcrumbs-total consumers.

There were very few adverse comments about any of the samples. The extruded samples were generally commented on as being ‘crispier/harder’ than the Morton's sample, however, there were some general observations that the Tech Centre samples had a bigger particle size than the Morton crumb, despite all the crumbs having been sieved to be the same size. This was probably attributed to the extruded samples absorbing more oil during cooking.

CONCLUSION

The characteristics of the sample extruded at 120°C (42810) showed bulk density and fat uptake properties that were more acceptable compared to the Morton's sample. Due to the significant difference, extruded superbake breadcrumb may be a suitable substitute for the Morton's breadcrumb. The study clearly showed that the good functionality of extruded breadcrumb was highly dependent on the extrusion processing conditions. Comparing the basic formulation of superbake breadcrumb (F2) and formulation (F15) for extruded breadcrumb, the extruded breadcrumb showed good functionality in relation to the control and considering further, the effect of ingredient on the texture of extruded breadcrumb, some ingredient can be excluded without adverse effect thus the crisp texture and maximum expansion of extruded superbake breadcrumb may be obtained by selecting the following extrusion processing conditions; Barrel moisture content 27%; Screw speed 150 rpm; Barrel temperature 120°C; Flow rate 55–61 kg/hr; Cut at die face. And a cost effective formulation comprising of wheat flour (88.7%); soy flour (5%); emulsifier (0.3%); salt (2%); baking powder (4%). On the basis of this study, extrusion cooking for the production of breadcrumb is recommended because with extrusion, some of the ingredient can be removed from the formulation without adverse effect probably due to the interplay between extrusion conditions during cooking. This thus reduces the cost of input. Similarly, less time is required for the process.

ACKNOWLEDGMENTS

The authors wish to thank Clough, B.; Fuller, A.; and Alcock, S. of British Sugar Technical Center for their technical assistance during the research.

Notes

Graduate student