Reduction of waste production during juice processing with a simultaneous creation of the new type of added-value products

Proper management of waste generated in food production is a significant problem in natural environment protection. Waste from food industry should be managed in a way that brings benefits, both ecological and economic [Girotto et al., 2015]. The present logistic strategies applied in the food industry are incapable of dealing with the hurdles of waste management. Incorporating technologies to derive value-added products, chemicals, and fuels is a positive step towards dealing with this problem [Ravindran and Jaiwal, 2016] Despite the constant development of new directions for waste management, it is also an important direction to limit their quantity by reformulating existing products and processing techniques. It is especially important, because food processing by-products are often rich sources of fibre and polyphenols, and their incorporation in the final product can bring nutritional benefits [Elleuch et al., 2011; Sudha et al., 2007].

It is unquestionable that fruit juices, due to the content of vitamins, polyphenols, minerals, and other valuable nutrients, are beneficial to human health [Markowski et al., 2015]. However, according to Oszmiański et al. [2007], health benefits are expected mainly in the case of cloudy juice consumption. On the other hand, irrespective of the form (clear or cloudy), fruit juices have a similar energy density and sugar content to sugar sweetened beverages: 250 mL of apple juice typically contains 110 kcal and 26 g of sugar; 250 mL of cola typically contains 105 kcal and 26.5 g of sugar [Gill and Sattat, 2014]. According to the Regulation of the European Parliament and of the Council [2011], the reference intake of energy and sugars are 2000 kcal and 90 g per day, respectively. Thus, it is evident that while the energy intake associated with the consumption of fruit juice portion is relatively low (for apple juice 5.25% of the reference intake), intake of sugars is much higher (for apple juice reaches even 28.8% of the reference intake). Moreover, WHO published a strong recommendation that for a person of healthy body weight, consum ing approximately 2000 calories per day, less than 10% of the total energy intake should come from free sugars, which is equivalent to 50 g (a glass of apple juice covers more than 50% of this amount). Additionally, the reduction to less than 5% of total energy intake would provide additional health benefits (in such case, a glass of juice will cover the total daily recommended portion of 25 g of free sugars) [WHO 2015]. According to the newest recommendations of WHO, the intake of sugars can be reduced by limiting the consumption of foods and drinks containing high amounts of sugars. In the list of such products, fruit juices are also mentioned: sugary snacks, candies, and sugar-sweetened beverages (i.e., all types of beverages containing free sugars – these include carbonated or non-carbonated soft drinks, fruit or vegetable juices and drinks, liquid and powder concentrates, flavoured water, energy and sports drinks, ready-to-drink tea, ready-to-drink coffee and flavoured milk drinks) [WHO 2014, WHO 2018]

When combining this information with the fact, that during the last decade, consumer requirements in the field of food production have changed considerably, and they duly believe that food contribute directly to their health [Bigliardi and Galati, 2016], it becomes obvious that fruit juices with such high sugars’ content are becoming less popular. Gill & Sattar [2014] stated that the accepted guidelines recommending the consumption of 5 portions of fruit and vegetables per day should not include fruit juices. Indeed, in the currently published recommendations, this list contain only ‘fruits and vegetables’, excluding potatoes, sweet potatoes, cassava and other starchy roots, and not mentioning juices [WHO 2015]. It has been shown that although consuming a significant amount of whole fruit reduces or neutralises the risk of diabetes, drinking large amounts of fruit juices may cause an increased risk of type 2 diabetes [Muraki et al., 2013]. Thus, every method that makes possible to reduce the amount of sugars in fruit juices can positively affect the consumers’ perception of juices.

Among the methods that can be used for the fractionation of liquid foods, membrane techniques have an important place [Bhattacharjee et al., 2017]. Depending on the type of the process, it is possible to separate: macromolecules, colloids, and microorganisms from the rest of soluble compounds (microfiltration MF); insoluble solids, macromolecules, and proteins from sugars and salts (ultrafiltration UF); sugars from salts (nanofiltration NF). Moreover, membrane techniques are low-temperature, environmentally friendly operations, and offer other important advantages, which make them increasingly popular in food processing: less manpower requirement, greater efficiency and shorter processing time than conventional filtration [Bhattacharjee et al., 2017].

In fruit juice industry, UF is usually applied in the clarification step without changing the temperature and pH of the solution and without chemical additives, thus reducing production costs, improving the product quality, and reducing labour costs [Urosevic et al., 2017]. However, as was mentioned above, cloudy juices are more beneficial to human health, and nowadays, consumers are becoming more and more interested in such a form of fruit juices. In the production of cloudy juices, there is no clarification step, which makes possible to retain some valuable ingredients in the final product. Moreover, the treatment of valuable cloudy fraction as a waste, as it is done in the traditional juice processing, do not fit well with the sustainable food processing. The proposed juice UF treatment, when implemented into industry, would give the benefit of reduced waste during juice processing.

Recently, UF was proposed for the preparation of cloudy apple-cranberry juice of reduced sugar content [Samborska et al., 2018]. In this approach, during the UF carried out in a batch mode, sugars were transmitted to the permeate (clarified juice), with the simultaneous rejection of colloids, high molecular weight compounds and fine particles in the retentate. As a result of such a treatment, the percentage of the reference intake of sugars associated with the consumption of 250 mL portion of the obtained product was reduced from 27.0% to 20.7%. At the same time, the cloudy fraction was concentrated.

The aim of this work was to investigate: 1) the possibility to obtain cloudy apple and apple-beetroot juices of reduced sugar content and concentrated cloudy fraction, 2) the physicochemical properties of the obtained products.

The purpose of UF in this work was to retain in a cloudy juice (retentate) the valuable compounds coming from fruit pulp, with simultaneous partial removal of sugars with permeate stream (clear juice). Thus, the presented approach was opposite to the commonly conducted research, focusing on the juice clarification, in which a clear juice is a final product. UF was carried out until the complete stop of permeate flux, which was the result of membrane fouling. In the case of apple juice, it was 120 min, while in the case of apple-beetroot juice – 80 min. In both processes, from 10 L of feed juice, 4 L of retentate was obtained, so the volume reduction factor (VRF), defined as the ratio between the initial feed volume and the volume of resulting retentate [Cassano et al., 2007], was equal to 2.5. This value was much lower than usually obtained during the UF, leading to juice clarification. Normally, clarification aims to recover as much of juice in the permeate as possible, and to concentrate total dissolved solids in the retentate as much as possible. He et al. [2007] investigated the clarification of apple cloudy juice by UF (the plate membrane sheets used were made of polyetersuphone with MWCO 50 kDa), and high VRF (> 20) was achieved. On the contrary, Cassano et al. [2007], ultrafiltrating kiwifruit juice with 15 kDa membranes, after 350 min obtained VRF of 3.75.

3.1

Characterization of feed juices, permeates and retentates

Apple cloudy juice (AJ), apple cloudy juice permeate (PAJ), apple cloudy juice retentate (RAJ), apple-beetroot cloudy juice (ABJ), apple-beetroot cloudy juice permeate (PABJ), and apple-beetroot cloudy juice retentate (RABJ) were subjected to physicochemical determinations. The results of these determinations are summarized in Table 1.

Table 1

Total soluble solids (TSS), glucose (G), fructose (F), total sugars (TS), non-sugar soluble solids (NSS), density (D), total acidity (TA) of apple cloudy juice (AJ), apple cloudy juice permeate (PAJ), apple cloudy juice retentate (RAJ), apple-beetroot cloudy juice (ABJ), apple-beetroot cloudy juice permeate (PABJ), and apple-beetroot cloudy juice retentate (RABJ), total colour difference (DE)

	AJ	PAJ	RAJ	ABJ	PABJ	RABJ
TSS [°Brix]	11.0±0.1c	8.8±0.0 a	9.2±0.1 b(0.66)†	11.4±0.0 b	8.6±0.0 a	8.7±0.1 a(0.68)
G [g×100 g−1]	2.1±0.1 c	1.6±0.0 b	1.8±0.1 b(0.68)	1.6±0.0 b	0.6±0.0 a	0.6±0.0 a(0.84)
F [g×100 g−1]	6.5±0.2 d	5.2±0.1 c	5.4±0.1 c(0.66)	4.3±0.1 b	3.4±0.1 a	3.6±0.1 a(0.66)
TS [g×100 g−1]	10.4±0.1 c	8.2±0.1 b	8.8±0.2 b(0.67)	8.2±0.1 b	5.6±0.1 a	5.8±0.2 a(0.71)
NSS [%]	0.6±0.0 b	0.6±0.0 b	0.4±0.0 a(0.58)	3.2±0.0 d	3.0±0.0 c	2.9±0.0 c(0.69)
TA [g×100 g−1]	0.41±0.0 c	0.25±0.0 a	0.37±0.0 b(0.74)	0.40±0.0 b	0.31±0.0 a	0.33±0.0 a(0.67)
ΔE	-	19.4	4.2	-	35.5	8.2
D [g×mL−1]	1.041±0.000c	1.034±0.000a	1.035±0.000b	1.044±0.000c	1.034±0.000a	1.036±0.000b

†

in brackets: recovery factor of certain compounds in retentates

a-c

the differences between mean values of certain parameters of feed juices and its UF products marked with different letters were statistically significant, for each juice and parameter separately

After the UF of AJ, the content of soluble solids (TSS) in R was significantly higher than in P, but lower than in the feed juice. In the case of ABJ, there was no significant difference between TSS content in P and R; at the same time, both values were significantly lower than in the juice not subjected to the UF process. The decrease of TSS content in the retentate compared to the juice resulted from the dilution with some amount of water remaining in the installation after the washing process, and the lower TSS content in P than in R resulted from selective membrane properties.

As the aim of this work was to obtain juices of reduced sugar content, the most important parameter to compare is TSS of juice before and after UF. In both juices, TSS of retentates was lower than of feed juices. P was characterized by a significantly lower density as compared to R. It was a result of the clarification process and the selective rejection of solid components.

The colour parameters of the tested juices differed depending on the type of juice. Moreover, there was a perceptible and significant colour change after UF, which led to the juice colour becoming lighter in permeates, and darker in retentates (Fig. 1). In the case of ABJ, the value of parameter a* increased significantly in permeate, that is, the share of the red colour increased compared to the juice. In both juices, there was a significant decrease in the value of parameter b* in the permeate compared to the juice, which indicated the shift towards blue colour.

Figure 1

Total colour differences ΔE indicated the magnitude of the colour difference between the juices and UF products. DE for retentates was lower than for permeates, which resulted from the clarification process affecting the great difference in the colour of permeates. Retentates were more similar to juices, because they contained the cloudy fraction. The complete rejection of suspended solids in retentate after cloudy juice UF was also demonstrated by Cassano et al. [2007] after kiwifruit clarification by 15 kDa membrane.

The new method for the reduction of waste production during juice processing was proposed: ultrafiltration process was used for cloudy juices’ reformulation (apple and apple-beetroot), in a manner opposite to the traditional juices’ membrane processing. Usually, UF is applied at the clarification step to remove cloudy fraction (treated as a waste) during clear juice production, which is not a sustainable approach. In the proposed method, UF was used to reject/concentrate cloudy fraction, with the simultaneous removal of some amount of sugars. It led to obtain a new type of juice, characterized by reduced sugar content and concentrated cloudy fraction. Due to potential health benefits of the consumption of cloudy juices as compared to clear juices, these types of obtained products can be described as pro-health, value-added products. The proposed approach also gives the possibility to reduce the waste production during juice processing.