The application of HHP in foods

1.3.3.1 Consumer acceptance

The perception of a preservation technique is an integral part of consumer’s acceptance towards a new product. In a study toward the consumer’s attitude about novel, nonthermal processing techniques, it was found that the concern toward HHP was rated almost equal to thermal processing, whereas concerns about radio frequency sterilization or irradiation were much higher (Table 5).

Consumers were found to generally have a more negative attitude towards foods processed by novel food processing techniques (i.e. without description of the technology). Interestingly, additional information about HHP technology and its benefits could significantly increase consumer acceptance.

16 INTRODUCTION

As such, it was argued that food industry would not encounter much resistance of the general public in the marketing of HHP-treated food (Cardello, 2003 from Wright et al., 2007).

1.3.3.2 Effects of HHP processing on foods

One of the most quoted benefits of HHP processing as preservation techniques is that it allows for the inactivation of pathogenic/spoilage microorganisms while leaving food quality attributes mostly intact.

Although there is a great deal of reports where no negative effect of HHP on the quality attributes of foods could be detected (Vercammen et al., 2011, del Olmo et al., 2014, Stratakos et al., 2015a), this statement is only in part true since important food quality factors such as colour, flavour, texture, and nutritional value can be negatively influenced by HHP treatment (Bermúdez-Aguirre and Barbosa-Cánovas, 2011, Buckow et al., 2013, Lingham et al., 2016). Generally, the greater the pressure level and time of application, the greater the potential for changes in the appearance of selected foods. A short summary of different pressure effects on food quality attributes is provided below.

Colour is an important determinant of consumer acceptance and the colour of different food products have been reported to be affected negatively under pressure. For example, HHP processing of raw meat causes discolouration, which gives it a cooked appearance. This change in colour is described to be the result of two processes (Ludikhuyze and Hendrickx, 2006); (i) whitening in the pressure range of 200 to 350 MPa, argued to be the result of globin denaturation or haem displacement/release. (ii) A loss of red colour caused by oxidation of ferrous myoglobin into ferric myoglobin (Fe²⁺ → Fe³⁺) at or above 400 MPa. HHP processing of raw turkey breast resulted in a significant colour change at pressures just below 300 MPa (1 min, 20 °C; Figure 3a; Tintchev et al., 2010). A pressure treatment of smoked salmon also results in a cooked appearance, though critical colour changes were not observed until a pressure level of 500 MPa (1 min, 20 °C; Figure 3b). The different colour stability of meat and smoked salmon under pressure are most likely the result of differences in the pigment substance and its stability in salmon (astaxanthin) and meat (myoglobin). In contrast to smoked salmon, 150 MPa (30 min, 1-5 °C) was determined as the maximum pressure parameter which did not negatively change the colour of fresh salmon (Amanatidou et al., 2000). This indicates that prior product processing can change the stability of food quality attributes under high pressure: a phenomenon also described for raw and cooked meat products (Pandrangi and Balasubramaniam, 2005).

Table 5: Consumer concern about food processing techniques. Percentage of respondent that were “very” or “extremely”

concerned with foods processed by novel techniques. Adapted Adapted with permission from Wright et al., 2007.

Copyright © 2008, John Wiley and Sons.

Food processing method % very of extremely concerned

Genetically modified 54

Irradiation 49

Radio frequency sterilization 40

High pressure treatment 20

Microwave processing 18

Thermal processing 18

Heat pasteurization 13

INTRODUCTION 17

Many colour changes and other food quality attributes are related to food enzymes. HHP processing can also positively influence food quality by the inactivation of enzymes that have a negative impact on the food product. Pressure can affect these enzymes in several ways, including (Ludikhuyze et al., 2006) (i) reversible or irreversible, partial or complete inactivation resulting from conformational changes, (ii) the inhibition or enhancement of the enzymatic activity as a result of pressure-induced volume changes, (iii) a change in substrate susceptibility, (iv) or facilitate the enzyme-substrate interaction by pressure-induced permeabilization of cellular membranes. For example, polyphenoloxidase, the enzyme responsible for enzymatic browning of damaged or sliced fruits and vegetables, can be (partially) inactivated by HHP processing (Ludikhuyze et al., 2006). The commercial production and preservation of sensory attributes of avocado’s or guacamole by HHP processing is, to a certain extent, based on the inactivation of this enzyme. Enzymes not only affect food colour but also texture and flavour. The enzyme pectinmethylesterase is involved in the loss of texture in fruit juices and vegetable sauces, and lipoxygenase causes a whole range of negative changes by oxygenation of polyunsaturared fatty acids. High pressure can be used for the inactivation of these and other enzymes related to food quality, but their inactivation differs greatly depending on the enzyme and both intrinsic (e.g. the presence of salts, sugars, additives, pH, etc.) and extrinsic factors (e.g. pressure temperature, time, etc.; Pandrangi and Balasubramaniam, 2005, Ludikhuyze and Hendrickx, 2006).

HHP treatments also can change the rheological or textural properties of foods. It was, for example, demonstrated that HHP processing (500 MPa, 5-15 min, 65 °C) of cooked sausages resulted in a less firm product when compared to their heat pasteurized counterparts (Mor-Mur and Yuste, 2003). In contrast, del Olmo et al., 2014 did not find any marked effect of HHP (600 MPa, 5 min, 4 °C) on the sensory characteristics of sliced “lacón” (cured–cooked pork meat product). Pressure treatment of smoked salmon at subzero temperatures (200 MPa, -18 °C) resulted again in a product with higher hardness, gumminess, and chewiness (Lakshmanan et al., 2005). In tomatoes, texture loss and cell rupture was observed at pressures between 200 and 400 MPa (Tangwongchai et al., 2000), whereas the texture of green peas was mostly unaffected at pressure up to 900 MPa (5-10 min, 20 °C; Quaglia et al., 1996). These examples merely illustrates the high diversity of product stability under high pressure and the necessity to examine food quality attributes before commercialization of HHP-treated food products.

a

b

Figure 3: HHP-induced colour change of foods. Colour change of turkey breast (a) and smoked salmon (b) by HHP processing (0–600 MPa, 1 min, 10 °C (turkey breast) or 20 °C (smoked salmon)). Adapted with permission from Tintchev et

al., 2010. Copyright © 2010, John Wiley and Sons.

18 INTRODUCTION