Fruit and vegetables are not consumed in the required quantities, throughout the world due to a variety of reasons e.g. availability, cost and/or convenience. Even though there importance is clearly defined by the World Health Organisation guidelines (Keenan et al. 2011a), in the developed world convenience is perceived as being the predominant cause for the demise of fruit and vegetable consumption. This has directly led to the development of a new product set – that enables the consumer to achieve the recommended 5 portions a day, whilst maintaining their busy life styles. ‘Smoothies’ have now entered into popular culture; the (Oxford English Dictionary, 2013) defines it as “Noun – a thick, smooth drink of fresh fruit puréed with milk, yogurt, or ice cream”
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A fruit Smoothie is a drink that blends fruit and fruit juice together to create a healthy snack. The Smoothie market to have reached $9.0 billion by 2015 (Global Industry Analysts, 2010) and that UK sales reached 34 million in 2006, which is 6.3 million up on 2001 according to Mintel who also expect Smoothie sales to treble by 2011 (BBC News, 2007). In the USA the sales reached $2 billion in 2012, which has grown 80% over the past 5 years (Smoothie Statistics, 2012). In the UK, the sales of smoothie increase to 80 million in 2007, but showed a reduction in sales gradually falling by 2009, however sales have increased again by 2011 to 55 million (British soft drinks, 2011).
Mintel are a company that provide food and drink research to the UK. They have reported that many fruit Smoothies have been found to have a hidden sugar content to sweeten the Smoothie up; many of the fruit Smoothies were found to have hidden sugars comprising of fruit juice concentrates and high fructose syrup (Courier mail, 2013). Most Smoothie’s have apple and banana as core ingredients. Apples have a natural sweetness; this means not as much, if any additional sugar needs to be added to the drink, to sweeten the taste, banana is also added as it adds a natural thickness to the Smoothie, nothing artificial needs to be added to the Smoothie (Innocent drinks, 2013).
One problem that is faced is the texture of the drink, it can be quite bitty or grainy, this is derived from tiny particles that some fruits contain, for example strawberries have small pips on the outside of the fruit, so blending the fruit alone will not get the particles to break up. However a way to change this has been found that passing ultrasound waves into the fruit during its preparation makes the particles smaller. Ultrasound wave technology has been available for many years, but in the last 10 years the food industry has developed a methodology to use the ultrasonic waves in food processing (Ultrasonic innovations, 2008). This paper presents an example of using ultrasound waves in the Fruit Smoothie product to reduce the particle size problem outlined earlier. There are a number of advantages for using ultrasonic waves, they have a more effective mixing and micro-mixing, faster energy and mass transfer, reduction in temperature – the mixture can remain at the same temperature throughout the process. Ultrasound wave technology also increases the production volumes of the Smoothies (Chemat et al., 2011).
To investigate and reduce the particle size within the Fruit Smoothie mixture using ultrasound waves.
To test the treated Smoothie for its- viscosity, colour and centrifuge for the acceptability of the particle size.
Testing the treated Smoothie on samplers – for the acceptability of the particle size, the colour and the taste in the mouth.
Employ ultrasound waves at different power levels for the reduction of particle size and for two different lengths of time.
To use the Brookfield viscosity to test the flow rate of the different samples. To use the Hunter LAB to analyse the intensity of the colour change and the centrifuge machine to test the separation for the different samples.
Test the finalised product on random, untrained samplers to identify their thoughts about the product and compare the product to an untreated sample product.
This paper will be an experimental hypothesis. Using ultrasound waves will reduce the particle size in the Smoothie product and create a smoother taste.
2. Literature Review
The literature review consists of what a Smoothie is, the types of products available, the role of ingredients, the manufacturing process and sensory attributes.
2.1 Smoothie Definition
The word Smoothie comes from the English word smooth meaning tender and creamy. Smoothies are defined as a creamy cold drink which is made of blended fruit or berries together with some fruit juice, only natural ingredients are added to the product. The texture of a Smoothie is of a thick consistency unlike the slush drink and has a consistency more like a milkshake (Smith et al., 2013).
2.2 Types of Smoothies Available
The main Smoothie manufacture that is available in the UK, is Innocent Smoothies, they have a wide range of Smoothies already available on the market, from Strawberry and Banana to Kiwi’s, Apples and Limes to Pomegranates, to Blueberries and Acai (Innocent Drinks, 2013). These Smoothies are available in four different sized bottles, they vary from handy grab and go bottles, to bottles that can be stored in the fridge and used many times over. Innocent dominate with 80% of the market in 2010 (Mintel, 2010).
Figure 1: Innocent Smoothie Drinks (Innocent drinks, 2013)
Innocent Smoothie also offers other products in this range, five ‘kids’ Smoothies are available in handy lunch box sized cartons, useful for lunches.
Figure 2: Kids smoothies (Innocent drinks, 2013)
Happy monkey are another brand of Smoothie that are mainly branded for kids and their lunch boxes (Happy Monkey Smoothies, 2013). They come in two varieties orange & mango and strawberry & banana, and can be purchased in a variety of shops. Happy Monkey Smoothies offer less variety than Innocent Smoothie however they have similar products available. One close to the orange and mango is available in Innocent’s children’s range and the strawberry and banana is found in the main Smoothie range.
Figure 3: Happy Monkey smoothie products (Happy Monkey Smoothies, 2013)
Another place that Smoothies can be found is from Ella’s kitchen, these again are more aimed at children to take to school and have as a healthy snack. They are comprised of five different flavours available in small handy sizes. Like Innocent and Happy Monkey, they have similar flavours with the same ingredients as the back bone to the Smoothie products.
Figure 4: Ella’s kitchen Fruit Smoothie products (Ella’s Kitchen, 2012)
The Naked Smoothie Company are aimed at producing Smoothies for adults on the go, that do not have time to eat fruit with their everyday life commitments. Naked advertise that they are a healthy alternative and contain antioxidants in them (Naked Juice, 2013). These advertisements are aimed at those wanting to try and stay healthier for longer by adding antioxidants into their bodies, to help fight free radicals. Naked have launched additional products that claim to increase energy levels throughout the day
Figure 5: Naked Juice Smoothies (Naked Juice, 2013)
These are the main Smoothie brands on the market in the UK today. Many companies target their brands towards children’s health, helping them get their 5 a day, thus making it easier for their parents by allowing them to have one of their products, the parent does not have to try and persuade the child to eat a piece of fruit. However some companies do promote their products to the older generation advertising that their Smoothie can help them to stay fit and healthy as well as their children. All these Companies claim that their products are 100% pure fruit without any added sweeteners or artificial flavourings.
2.3 Role of ingredients
Fruit is the primary component in a Smoothie. Many producers of fruit Smoothies promote how they can help you achieve your five a day in a tasty quick convenient drink.
Strawberry: Strawberries in this fruit Smoothie is one of the main ingredients and adds flavour to the drink. Strawberries have a natural sweetness that will sweeten up the product without the need to add any sweeteners to the mixture, thus making the smoothie healthier. Strawberries are a major contributor and they give the drink the pink colour. Strawberries have natural bits around them which give the texture in the smoothies the natural graininess; this is what the ultrasound waves will reduce in the smoothies.
Banana: As well as bananas being one of the main ingredients in the smoothie, banana is also a natural thickener (Innocent Smoothie, 2013), this making the banana a vital ingredient in the fruit mixture, as without the banana the drink may become too runny. The banana also adds as a bulking ingredient as it increases the volume of the Smoothie. As banana is one of the main ingredients it adds to the flavour of the drink and produces the banana and strawberry flavoured Smoothie.
Grape: Grape juice adds to the flavour, and helps break down the thickness of the banana and sweetens the banana taste. Grape is an acidity regulator and controls the acidity levels in the smoothie. Without the grape juice the acidity in the Smoothie may become too strong.
Apple juice: Apple juice is used to add a natural sweetener to the Smoothie (Innocent Smoothie, 2013). By adding this it means no additional sugar is necessary resulting in a healthier drink. The apple juice as with grape helps to break down the banana thickness to create a smoother texture.
Oats: Oats are added to the fruit Smoothie to add more fibre. They also change the thickness of the product. The oats added in to the mix changes the texture of the Smoothie. This again will be decreased by using ultrasound technology to reduce the particle size.
2.4 Manufacturing Process
Ultrasound is a non-thermal technology utilising high power and high frequency that results in a longitude wave that creates a sudden implosion of bubbles. The implosion generates localised spots with a very high pressure that can disturb cellular structures; this means the particle size will reduce (Fellows, 2009). When ultrasonic waves hit the surface of a material they generate a force, this force is vertical to the surface and it results in a compression wave that moves through the food. If the force is parallel to the surface it produces a shearing wave. Both methods allow the food product to be sonicated (Fellows, 2009). In recent years using ultrasound waves in food processing has been investigated extensively (Rawson et al, 2011) concentrating on the effect that pulses have on the nutritional aspects of the food sample and the lengthening of the shelf life of products. Sonication has significantly improved the preservation role in foods (Rawson et al., 2010). The amount of bubbles produced depends on the amount of frequency and amplitude of the ultrasound waves (Keenan et al., 2011b). This means the particles of the fruit Smoothie should be reduced when the ultrasound waves are at a higher frequency and higher amplitude. The longer the ultrasound waves are placed through the Smoothie the more this will have an affect the amount of particles broken up.
2.5 Quality attributes
Fruit and vegetable beverages can have certain sensory barriers that can put off many people from drinking them. These barriers include a bitter taste and a grainy texture and in the most recent National Diet and Nutritional survey (NDNS) report, it highlights the difference in consumption of the 5 portions of fruit and vegetables per day between children and adults. It found that children are more prone to eating fruit and vegetables every day. Fruit juices continue to grow in popularity and are potentially driven by an increase public interest in ‘preventative healthcare’ (Wootton-beard and Ryan, 2011).
Due to marketing and advertisement of Smoothies there is a misconception that the drinks are as healthy for you as eating fruit by themselves. Labels claim that they are packed with vitamins, low in fat and bursting with goodness and the UK has spent over £100 million a year on Smoothies, however many of them contain sugar, calories and acids as extra ingredients that have been added to sweeten them up and make them taste better (BBC News, 2008). This means that Smoothies are not as healthy as the packaging is advocating. Juicing fruit and storing it can make it quite acidic, and one being consumed can damage the person’s teeth. Juicing takes away the fibre and removes many nutrients that are found in the whole fruit (Independent, 2006).
Juice and Smoothies count as one portion of your 5 a Day when drunk in a 227g portion. It was found that pure fruit and vegetables can offer similar health benefits to whole fruit and vegetables. This is due to the antioxidant and polyphenol content that is found in fruit and vegetables, however it still remains a concern regarding the impact juices have on sugar consumption, fibre intakes, dental health and appetite control. It has been found that fruit contains a naturally high carbohydrate, sugar, starch and fibre content. Smoothies are not that different to a consumer choosing fruit like a banana than it would be if they chose it in the Smoothie form (Ruxton, 2008). The advice expressed by health professionals is that consumption of Smoothies should be discouraged due to the high carbohydrate and sugar content, as this would prevent the rise in sugar consumption that has been on the increase in recent years. However this is a mistaken belief in regards to Smoothies, for in a 250ml portion, 30g of sugar can be found, similar to a piece of fruit. Research has been undertaken to show that Smoothies may have more associated dental health problems than eating two portions of whole fruit and vegetables; this has not been proven with reliable evidence.
When Fruit Smoothies were first introduced onto the market, it was thought that it would encourage those in the population who did not consume the minimum daily dietary requirements regarding fruit and vegetables. It was a concern that they may stop people from consuming the actual fruit and vegetable however, it was found that those who consumed higher levels of fruit and vegetables were more likely to consume both the whole fruit/vegetable and Smoothies/fruit juices. Smoothies were found to be higher in fibre, vitamin C and antioxidants compared to fruit juices alone (Ruxton, 2008).
2.7 Consumer acceptability/ Sensory
To the consumer, the most important quality attributes are the five sensory characteristics – Texture, Flavour, aroma, shape and colour (Keenan et al., 2011b). These attributes determine the individual’s preference for specific products. These attributes help to define differences between certain brands and their differing tastes. In the case of this study, these attributes will help the panellists to taste the size of the particle in the sonicated Smoothies (Povey and Mason, 1998).
2.8 Taste and Flavour
Taste and flavour is a major factor in consumer choice. There is a difference between taste and flavour, taste is the sweetness, sourness, saltiness, bitterness and umami. The taste buds on the tongue affect what the taster can detect, and some attributes can be detected at very low thresholds in certain food groups. Taste occurs on the tongue were 10,000 taste buds are located on the front, back, sides and the tip of the tongue. Each taste bud has clusters of 50-100 taste receptor cells.
Flavour is the result of the interaction between the sense of smell that the person can detect from the sample, and the taste that the taste buds have given off which determines the flavours they can taste in the sample, however 80% of the perception is from the smell of the sample, the food is inhaled through the nostrils and from the back of the mouth as the food is chewed and swallowed. The flavour of foods is influenced by the flavour compounds which are released when chewed (Povey and Mason, 1998).
The texture of food has a major influence on consumer’s perception of quality. Information is passed to the brain, about the texture of the food from the sensors in the mouth and from recalling these senses from memory it can build up an image of the texture properties of the food. This can be seen in three stages:
1. Initially the first stage is to assess the hardness, the ability to break the food and the consistency of the food product in the first bite
2. The second stage is the chewiness, adhesiveness and the gumminess during the chewing of the product. During this phase the moistness and the greasiness of the food is also detected.
3. The third stage is the perception of the rate at which the food will be broken down whilst chewing. The ‘type’ of the pieces formed, then the release of moisture and finally any coating on the mouth or tongue with food (Povey and Mason, 1998).
The colour of a Smoothie or any other product is one of the main aspects that a consumer is going to take into consideration when choosing a product they wish to purchase.
If the colour is unusual or not natural to the eye, consumers may find it off putting, particularly in this market segment, as the Smoothie purports to be a replacement for natural products. So the products colour is very important
The colour of a Smoothie is affected when the sonic processing is undertaken. Typically the more ultrasound power put into the Smoothies, the more particles are broken up, resulting in the colour of the Smoothie being affected by the particle degradation (Keenan et al., 2012a).
The methodology section consists of the following: Sample Preparation, Ultrasound Processing, Physical analysis, Brookfield Viscosity, Colour, Analysis, Centrifuge Analysis, Sensory Analysis, Ethical Issues, and Statistic Analysis.
As similar work has been undertaken on the topic of using ultrasound waves in Smoothies, several methods were incorporated to expand on the work already developed to test four different methods (Keenan et al., 2010), (Keenan et al., 2011a), (Keenan et al., 2012b), (Keenan et al., 2012c). As this paper is concentrating more on the mouth feel of the Smoothie, than for example the shelf life changing due to the sound waves being passed through the product, the sensory aspect was a higher priority, so only following limited methods helps to get the full purpose of the study across.
In this study, a Smoothie is the product of choice to test and investigate with the ultrasound wave’s process, because of the varying particle size that can be found in Smoothies. Reducing the particle size should have effective results. According to recent sales, Smoothies have become very popular in the UK, however many consumers find the graininess of some fruit puts many consumers of drinking Smoothies off putting. This study, investigates a way to reduce this, using a novel technology that has not been used extensively in food products.
3.1 Sample preparation
The Smoothies prepared were based on the commercially available Smoothie Strawberry and banana by innocent Smoothies. 1400ml of Smoothies was made using 288g of banana, 284g of grapes (mixed), 520g strawberries were chopped, 700ml of apple juice from concentrate then added to a homogeniser (Keenan et al., 2010), (Keenan et al., 2011a) and (Keenan et al., 2011c) along with 50g of oats, and all food products were sourced from a local supermarket. Once the fruit, juice and oats are homogenised the Smoothie is split into seven 250ml samples and refrigerated to between 2-4oC, so all Smoothies are at the same temperature before ultra sound processing can take place. Each time the particles are tested the same amount of each fruit is the same, to make sure texture and colour is the same each time. The Smoothie composition was derived from the commercially available; innocent Smoothie product – banana and strawberry.
Place into blender with oats and apple juice for 1 minute
Split mixture into seven samples
Chop strawberries and bananas.
Place 2 into ultrasound machine for 5 and 10 mins. on power 60
Place 2 into ultrasound machine for 5 and 10 mins. on power 100
Place 2 into ultrasound machine for 5 and 10 mins. on power 20
Test sonicated samples for separation of particles
Test sonicated samples for colour
Test sonicated samples for viscosity
Figure 6: Summary Flow Chart of Smoothie Method of Sonication and Testing.
3.2 Ultrasound machine
Once the Smoothie is split into portions the ultra sound treatment can be done, the Smoothies were tested using (Keenan et al., 2011a) method on how to test ultrasonic waves through fruit samples. Three treatments were used in this practical; the Smoothies were treated with three different power levels (20%, 60%, 100% on the 0.5 cycle) for two different lengths of time. Six of the Smoothie samples were processed on and one was kept as a control to compare the results to the original Smoothie.
Figure 7: Ultrasound Machine
3.3 Physical Analysis
Once each of the Smoothies has been treated, tests were done on the different samples for viscosity, colour and centrifuge.
3.4 Process Parameters
Due to the ultrasound machine being placed in to the smoothie, it can change the temperature of the smoothie mixture. (Keenan et al., 2012a) study shows that the smoothie mixture inside the pressure chamber increased from 20 to 37oC during the high pressure processing.
Table 1: Processing power level and time it was sonicated
A way to stop the temperature of the Smoothie being increased when ultrasound waves are being passed through it, is to decant the mixture into a beaker (which allows water to flow through) syphon off the warmer water so as to keep the Smoothie from increasing in temperature.
3.5 Brookfield Viscosity
Viscosity is a measurement of the internal friction of a fluid, for example liquids and semi solids and Brookfield is the measurement of these. The viscosity measurements are made to test the quality and the efficiency of a product. A main way that that researchers test their work, is using a viscometer. It is one of the quickest, most reliable and accurate ways of analysing some of the most important factors affecting the product. (Brookfield engineering, 2013)
The accuracy of the viscometer was checked with a standard solution of water to calibrate the viscometer. The seven samples were then tested the same way this was done by using the number four spindle at speed ten and placing the spindle into the Smoothie sample to get readings. A reading was taken on twelve occasions at ten second intervals to get an average. This was repeated on all seven samples.
Figure 8: Brookfield viscometer meter
3.6 Colour Analysis
The hunter lab model UltraScan PRO was used to test the changes in colour of the fruit Smoothies once the initial processing had taken place. The colour test was useful to see if the Smoothie had become lighter or darker in visual terms after the processing.
Hunter Lab system is a popular and trouble free technique used in both quality control and research; it is able to test a wide spectrum of product colours from transparent films to clear liquids and/or opaque solids (hunter, 2008). In this case study it was used to test the difference in colour of the six processed samples, comparing them with the control sample.
The colour was then tested by placing some of the Smoothie into a glass square tube with black foam to form a blackout around the outside to avoid any other light affecting the result. This was then placed on to the machine and the machine produced an L* a* b* reading of the colour. Each time a new sample was tested it was calibrated back to the original Smoothie. Each of the seven samples was tested three times to obtain an average.
The 250ml Smoothies are then spilt in to 125ml samples. One 125ml sample is placed into the refrigerator and left for twenty four hours; the other 125ml placed into a water bath at 4oC for the same twenty four hours.
Figure 9: Hunter Lab ColourC:UsersFionaPicturesIMG_0487.JPG
3.7 Centrifuge Analysis
Centrifuge is driven by a motor and forces a sample to evenly separate the substance of greater and lower densities apart. A sample is placed in the machine and the motor is switch to a certain speed, the sample is then spun around a fixed axis.
After the twenty four hours, 10ml of each is poured into a numbered tube and then placed into a centrifuge machine and spun at 4600rpm for ten minutes, this causes substances to separate and the bigger particles at the bottom with the smaller particles on top. The results are entered and analysed using SPSS.
Figure 10: Centrifuge machine
3.8 Sensory Analysis
Four samples of 1000ml were poured into four jugs consisting of Strawberries, banana, grapes, apple juice and oats. Three of the samples were treated with ultrasound waves at three different power levels (20%, 60%, 100% on cycle 0.5) for 10 minutes and the fourth was kept as a fresh control sample. The samples that were being tested were treated at the three different power levels for 10 minutes and control sample that was left untreated.
An untrained panel of 50 people with an age range of 19 to 57 were used. As the study was based on the overall mouth feel of the Smoothie no training was needed before the tasting took place. The sensory was carried out in individual sensory booths and had controlled lighting. The odour in the booths was controlled to avoid any misconception of the product and its taste.
The panellists were presented with four samples of the different Smoothies and given a sample of 10ml in 25ml plastic cups. Each sample was given a randomised three digit code, this was to avoid the panellist from know which order they are sampling each (Keenan et al., 2011b). Each panellist received the samples in a different order. The untrained panellists were given a cup of water to cleanse the palate, so the mouth was free of flavour before the next sample is tasted.
There were eight important attributes that were necessary to get a clear picture of whether the participants could tell the difference between the samples and if the particle size had been reduced. The sensory attributes being tested for were colour, smell, appearance, texture, mouth feel, viscosity, aftertaste, and over all acceptability. The rating scale used was a horizontal line scale. A vertical line is placed on the scale between 1 and 9 with the left to right on the intensity of liking the product, for example pale to dark.
Bits/ No Bits
Too thin/ Too thick
Table 2: Sensory Attributes of Smoothies
3.9 Ethical Issues
The only ethical part to this study that needs to be addressed is the sensory analysis. On taking part in the sensory analysis, the participants signed an agreement, that they understood the agreement, they understood the ingredients in the samples and made it known if any allergies or intolerances they had that would stop them from taking part in the study. All participants knew that they were free to stop taking part in the study at any point if they wished to so.
3.10 Data analysis
All values were repeated twice to get an average number to compare. The comparison was tested using SPSS (ANOVA, TTest) and Microsoft Excel Software. The difference was considered significantly different with a p value of <0.05.
The smoothies that had been processed with ultrasound waves were analysed and the results were measured and statistically analysed by using Microsoft Excel, and SPSS.
4.1 Hunter Colour LAB Analysis
The colour of the six samples of smoothies that were processed at different power levels and the control sample were analysed to see the colour change. The average readings of the colour parameters (L, a, b, TCD and Chroma) of each of the samples was calculated and can be seen in table below. The analysis was repeated three times to get an average, and all the tests were completed twice to check the acceptability of the results.
5 minutes 20% Amplitude
10 minutes 20% Amplitude
5 minutes 60% Amplitude
10 minutes 60% Amplitude
5 minutes 100% Amplitude
10 minutes 100% Amplitude
Table 3: The average on Lab at the different power levels
Figure 11: L values (a), a values (b), b values (c), TCD values, (d), and Chroma Values (e) of smoothie samples colour at the different level of processing.
See figure 11a, b, c, d, and e sample key in appendix 1.
Figure 11a, 11b, and 11c, has revealed that the more ultrasound waves that are placed through the smoothies, the more the colour of the smoothie changes. Figure 11d shows the total colour difference (TCD) in the Smoothie samples at different power levels.
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