Paired preference tests: ‘Liking’, ‘Buying’ and ‘Take Away’ preferences

Paired preference tests of liking require consumers to specify which of two foods are preferred or whether there is no preference. For ‘Buying’ preference tests, consumers specify which of two foods they are more likely to buy or whether there is no operational difference in likelihood to buy. The former test is designed to predict choice behaviour, the latter, buying behaviour. To validate the predictive ability of such tests, consumer choice and buying behaviour should be observed for several months. Another approach is to allow consumers to take away some of the foods used in the test and observe what they take. Consumers of potato chips were required to taste chips whose flavour and appearance were obviously different. A first group (N = 109) were given a traditional paired preference test of liking. A second group (N = 108) were given a preference test of buying. A third group (N = 101) were given both tests. After the test, out of sight of the experimenter, consumers were presented with two rows of plain plastic ‘snack’ bags, filled with the chips used in the test. They could take away either two bags of the same type of chip (a ‘Take Away’ preference) or one of each type (no ‘Take Away’ preference) or take neither (rejection). ‘Liking’ preferences predicted what was taken away for only 48% of consumers for the first group and 45% (third group). For ‘Buying’ preferences, the correspondence was 56% (second group) and 60% (third group). Using buying tests separately or together with liking produced some differences. More reliably, approximately 60% of consumers in all groups chose one bag of each. ‘Take Away’ preferences suggested low predictability for paired preference tests of liking and buying. ‘Take Away’ preferences are not a substitute for following a consumer for several months but they are a step in the right direction.     

Non-destructive evaluation of quality and ammonia content in whole and fresh-cut lettuce by computer vision system

The paper describes the developed hardware and software components of a computer vision system that extracts colour parameters from calibrated colour images and identifies non-destructively the different quality levels exhibited by lettuce (either whole or fresh-cut) during storage. Several colour parameters extracted by computer vision system have been evaluated to characterize the product quality levels. Among these, brown on total and brown on white proved to achieve a good identification of the different quality levels on whole and fresh-cut lettuce (P-value < 0.0001). In particular, these two parameters were able to discriminate three levels: very good or good products (quality levels from 5 to 4), samples at the limit of marketability (quality level of 3) and waste items (quality levels from 2 to 1). Quality levels were also chemically and physically characterized. Among the parameters analysed, ammonia content proved to discriminate the marketable samples from the waste in both product's typologies (either fresh-cut or whole); even the two classes of waste were well discriminated by ammonia content (P-value < 0.0001).A function that infers quality levels from the extracted colour parameters has been identified using a multi-regression model (R² = 0.77). Multi-regression also identified a function that predicts the level of ammonia (an indicator of senescence) in the iceberg lettuce from a colour parameter provided by the computer vision system (R² = 0.73), allowing a non-destructive evaluation of a chemical parameter that is particularly useful for the objective assessment of lettuce quality.The developed computer vision system offers flexible and simple non-destructive tool that can be employed in the food processing industry to monitor the quality and shelf life of whole and fresh-cut lettuce in a reliable, objective and quantitative way.     

Chemical,instrumental and sensory characteristics of cooked pork ham

Instrumental, chemical and sensory parameters of cooked pork ham were evaluated. Principal component analysis was carried out on the basis of the instrumental variables related to colour and texture. The four PCs account for almost 94% of the total variance in the data set. The PCA only separated 3 hams with a¹ > 10. Hardness was correlated with non-collagen muscle protein (P ⩽ 0.01), gumminess (P ⩽ 0.01) and ash (P ⩽ 0.05). Sensory evaluated tenderness showed positive significant correlation with L¹ (P ⩽ 0.01). The most important colour parameter seems to be a¹, which was negatively correlated with sensory evaluated parameter colour (P ⩽ 0.01). The PCA performed on all parameters (sensory, chemical and textural) discriminated two groups of hams differing in non-collagen muscle protein content and hardness.     

Effect of pulsed electric fields on the structure and frying quality of “kumara” sweet potato tubers

The aim of this research was to study the effect of pulsed electric fields (PEF) on the microstructure of “kumara” sweet potato (Ipomoea batatas cv. Owairaka) and its quality after frying. Whole sweet potato tubers were treated at different electric field strengths ranging from 0.3 to 1.2 kV/cm with specific energy levels between 0.5 and 22 kJ/kg. Cell viability was determined using tetrazolium staining to investigate the uniformity of the PEF effect across tubers. Based on the patterns of viable cells it was observed that the effect of PEF was not homogeneous across the tuber. This result was also supported by the pattern of enzymatic browning due to PEF facilitating the reaction of polyphenoloxidase and phenols. PEF treatment resulted in significant softening of the ground tissues, but not on the dermal tissues, as determined by texture analysis. With respect to frying quality, tubers pre-treated with PEF at electric field strength of 1.2 kV/cm and fried at 190 °C had an 18% lower oil content than non-PEF treated samples. The kinetics of browning as a function of frying time could be described by a fractional conversion model. The activation energy (Ea) of the browning rate during frying increased (more temperature sensitive) due to PEF pretreatment at 0.5 kV/cm and 1.2 kV/cm. It implies that PEF pretreatment allows frying the potato chips at lower temperature in order to achieve the same brown colour intensity as the non-PEF treated tubers. This study shows clearly that PEF could reduce the energy required for cutting and frying of kumara.Industrial relevanceThis study provides evidence that the effect of PEF processing on whole kumara tubers is not uniform, demonstrating heterogenous distribution. These findings provide important information for food industry to design appropriate PEF processing conditions for solid materials. More importantly, PEF treatment reduced the energy required for cutting and frying of kumara, and reduced the oil content in the fried kumara chips.     

Microbial cells as colloidal particles: Pickering oil-in-water emulsions stabilized by bacteria and yeast

Thermally-inactivated baker's yeast (Saccharomyces cerevisiae) and lactic acid bacteria (Lactobacillus acidophilus and Streptococcus thermophilus) were used to generate and stabilize model oil-in-water (O/W) emulsions containing up to 80 wt.% dispersed oil. With optimized compositions, cell-covered dispersed oil droplets were stable against droplet coalescence and bulk phase separation for over four months. From a textural perspective, these emulsions were self-supporting and exhibited a mayonnaise-like consistency. The microbial cells acted as Pickering-type stabilizers by residing at the oil–water interface. The three-phase contact angle of the yeast at the oil–water interface measured using confocal microscopy was 30 ± 9°, demonstrating its ability to stabilize O/W emulsions. These microbial cells may be used in the design of processed food emulsions with an ‘all-natural’ designation as well as for the replacement of common synthetic surfactants to permit clean label declarations.     

Effects on Escherichia coli inactivation and quality attributes in apple juice treated by combinations of pulsed light and thermosonication

Pulsed light (PL) and Thermosonication (TS) were applied alone or in combination using a continuous system to study their effect on Escherichia coli inactivation in apple juice. Selected quality attributes (pH, °Brix, colour (L, a, b, ΔE), non-enzymatic browning (NEBI) and antioxidant activity (TEAC)) were also evaluated pre- and post-processing. Two PL (360 μs, 3 Hz) treatments were selected and the juice exposed to energy dosages of 4.03 J/cm² (‘low’ (L)) and 5.1 J/cm² (‘high’ (H)) corresponding to 51.5 and 65.4 J/mL, respectively. The juice was also processed by TS (24 kHz, 100 μm) at 40 °C for 2.9 min (L) or 50 °C for 5 min (H), corresponding to 1456 and 2531 J/ml energy inputs, respectively. The effect of the resulting four energy levels and sequence (PL + TS and TS + PL) was studied. When the technologies were applied individually the maximum reduction achieved was 2.7 and 4.9 log CFU/mL (for TS (H) and PL (H) respectively), while most of the combined treatments achieved reductions in the vicinity of 6 log CFU/mL, showing an additive effect for both technologies when acting in combination, regardless of the sequence applied. All treatments significantly changed the colour of apple juice and the sequence in which the technologies were applied affected colour significantly (P < 0.05). The energy level applied did not affect any of the measured quality attributes.     

The production and microbiological status of skin-on sheep carcasses

There is a demand by certain ethnic consumer groups in the United Kingdom for skin-on, singed carcasses, primarily from older sheep, but their production is illegal under current EU legislation. The aim of this study was to devise a protocol to produce carcasses having the desired ‘smoked’ colour and odour and an acceptable microbiology. A successful result could form the basis of a case to revise the legislation. Three key steps in the selected procedure were carcass singeing using specially designed gas burner equipment, pressure washing to clean the carcass and then evisceration. It was shown that a second heat application, termed ‘toasting’, if applied after evisceration, significantly (P < 0.001) reduced Enterobacteriaceae and TVC counts on carcasses before chilling. Microbiological quality was also improved when toasting was the final step, following carcass splitting and inspection. Carcasses produced in this way had significantly (P < 0.001) lower Enterobacteriaceae and TVC counts before chilling than conventionally dressed sheep carcasses produced in the same abattoir.     

Quality of ‘Abacha’ from Fresh Cassava Roots and Dried Chips

This study was undertaken to determine the possibility of producing acceptable ‘abacha’ from dried chips. The ‘abacha’ slices were processed from dried cassava chips and fresh roots of four cassava varieties, TMS 98/2101, NR/87184, TMS 97/4779 and NR87184. The proximate composition, chemical and sensory properties as affected by the processing method and variety were evaluated. The proximate composition of the ‘abacha’ (on dry basis) showed moisture content range of 9.53 – 10.48%, protein 1.07 – 1.66%, ash 2.06 – 2.56%, fibre 1.72 – 1.95, fat 0.39 – 0.58% and carbohydrate content of 83.59 – 85.05%. The chemical composition of the wet ‘abacha’ slices showed pH of 5.60 – 5.80, total titratable acidity (TTA) of 0.047 – 0.063, and hydrogen cyanide (HCN) value of 7.80 – 10.41 mg/100 g. Generally, the TTA of the ‘abacha’ samples was not significantly (p > 0.05) affected by the method of processing ‘abacha’ and the variety used. Drying the wet ‘abacha’ reduced the pH to 5.20 – 5.30, increased the TTA to 0.213 – 0.230% and further reduced the HCN content to 7.32 – 8.63 mg/100 g. The HCN of all the ‘abacha’ samples processed from dried chips were significantly (p < 0.05) lower than the HCN of ‘abacha’ processed from fresh cassava root in some of the varieties. The lower sensory scores for ‘abacha’ made from dried chips shows that they were inferior to the ones from fresh cassava, although they were also accepted by the consumers. It also compared favourably with the ‘abacha’ processed from fresh cassava root in chemical qualities. This shows that when the need arises ‘abacha’ slices can be processed from dried cassava chips.     

Sweetness and aroma perceptions in dairy desserts varying in sucrose and aroma levels and in textural agent

Sweetness–aroma interactions were investigated in model dairy desserts varying in sucrose concentration, aroma concentration and in textural characteristics using different textural agents (κ-, ι-, λ-carrageenans and an equal-mix of the three). Overall intensities of sweetness and aroma perceptions were evaluated by sensory analysis and apparent partition coefficients of aroma compounds were measured by static headspace—GC.Sweetness–aroma interaction was characterised by a non-reciprocal relationship. Concentration of aroma had no impact on sweetness intensity, whatever be the sucrose concentration or textural characteristics of desserts, whereas varying texture or sucrose concentration modified aroma intensity. However, effects on aroma assessment were effective only when aroma concentration was the highest. In this condition, use of λ-carrageenan or increasing sucrose concentration from 25 to 50 g kg⁻¹ enhanced aroma intensity, but no extra enhancement was observed when sucrose concentration was 100 g kg⁻¹. As the air–dessert partition coefficient remained constant, impact of textural characteristics and sweetness variation on aroma perception did not result from physico-chemical interaction.     

The ripening influence of two papaya cultivars on carotenoid biosynthesis and radical scavenging capacity

Carotenoid biosynthesis in papaya fruits from the cultivars (cv.) ‘Golden’ and ‘Sunrise Solo’ was studied throughout three different ripening stages. The content of these secondary metabolites was assessed using HPLC–PDA–MSⁿ. Carotenoid levels increased during ripening, with all-trans-lycopene varying from 0.73 to 1.58 μg/g in the cv. ‘Golden’ and from 0.68 to 1.67 μg/g in the cv. ‘Sunrise Solo’. The all-trans-β-cryptoxanthin content varied from 1.29 to 3.0 μg/g in the cv. ‘Golden’ and from 0.28 to 5.13 μg/g in the cv. ‘Sunrise Solo’. The Zds gene showed a different pattern of expression during the ripening and between cultivars, while the Lcyβ gene expression was up-regulated in the two cultivars. The capacity to scavenge peroxyl radicals did not show a significant difference among the ripening stages and between the different cultivars. This study describes, for the first time, a tentative correlation between carotenoid biosynthesis in papaya pulp and the gene expression of the enzymes related to this pathway.     

Effect of Pre-Drying and Hydrocolloid Type on Colour and Textural Properties of Coated Fried Yam Chips

The effect of pre-drying and coating on colour and texture of yam chips were investigated. The colour parameters studied were lightness index (L*), hue angle (h) and browning index (BI). Peak force (PF) of penetration was observed for texture. Coating pick-up (amount of coating adhering to the samples) prior to frying was determined and moisture content of fried samples was also determined. The type of hydrocolloids used in the coating formulation had significant (p < 0.05) effect on coating pick-up, initial moisture content and texture of the chips; while samples that were not pre-dried had higher pick-ups and moisture contents. Pre-dried samples were darker brown in colour and harder in texture than samples that were not pre-dried as evidenced by their higher browning index and peak force values, respectively, thus enhancing the colour and texture of the chips.     

Addition of seaweed (Laminaria digitata) extracts containing laminarin and fucoidan to porcine diets: Influence on the quality and shelf-life of fresh pork

A seaweed extract containing laminarin (L) and fucoidan (F) (L/F) was manufactured from brown seaweed (Laminaria digitata) in spray-dried (L/F-SD) and wet (L/F-WS) forms. The effect of supplementation of pig diets with L/F-SD and L/F-WS (L, 500 mg/kg feed; F, 420 mg/kg feed) for 21 days pre-slaughter, on quality indices of fresh M. longissimus dorsi (LD) steaks was examined. Susceptibility of porcine liver, heart, kidney and lung tissue homogenates to iron-induced (1 mM FeSO₄) lipid oxidation was also investigated. Dietary supplementation with L/F did not increase plasma total antioxidant status (TAS). In LD steaks stored in modified atmosphere packs (80% O₂:20% CO₂) (MAP) for up to 15 days at 4 °C, muscle pH, surface colour (CIE ‘L*’ lightness, ‘a*’ redness and ‘b*’ yellowness values) and microbiology (psychrotrophic and mesophilic counts, log CFU/g pork) were unaffected by dietary L/F. In general, levels of lipid oxidation (TBARS, mg MDA (malondialdehyde)/kg pork) followed the order: C > LF-SD > L/F-WS. A statistically significant reduction in lipid oxidation (P < 0.05) was observed in LD steaks from 75% of pigs (n = 6) fed with L/F-WS compared to controls. Iron-induced lipid oxidation increased in liver, heart, kidney and lung tissue homogenates over the 24 h storage period and dietary L/F-WS reduced lipid oxidation to the greatest extent in liver tissue homogenates. Results demonstrate potential for the incorporation of marine-derived bioactive antioxidant components into muscle foods via the animal's diet.     

Modelling kinetics of watercress (Nasturtium officinale) colour changes due to heat and thermosonication treatments

Watercress (Nasturtium officinale) colour changes due to blanching by heat and a combined treatment of heat/ultrasound (thermosonication) were studied in the temperature range of 82.5 to 92.5 °C. The application of thermosonication was intended to enable less severe blanching treatments and, therefore, improve the quality of the blanched product. The thermosonication blanching processes promoted changes of the green colour (aⁿ parameter) at a higher rate (P < 0.05), when compared with the heat blanching processes. No significant differences (P > 0.05) were detected between heat and thermosonication blanching processes in terms of the colour parameters Lⁿ, bⁿ and TCD changes. In both treatments, a fractional first order model fitted well the experimental data for Lⁿ, aⁿ and bⁿ (R_H² = 0.99; R_Ts² = 0.99) and TCD (R_H² = 0.92; R_Ts² = 0.96) colour parameters.The chlorophylls content showed no significant differences (P > 0.05) between thermally treated and thermosonicated watercress samples.The present findings will help to evaluate the effectiveness of thermosonication as a novel process to replace the classical heat treatment.Industrial relevanceConventional blanching commonly results in severe losses or destruction of nutrients due to process intensity and extended process times. Consequently, the attempts to use the synergistic effects of heat and ultrasound (at least) for enzyme inactivation are of high relevance. The results, although not conclusive, indicate, that they may aid optimization of blanching processes.     

Prediction of beef eating quality from colour,marbling and wavelet texture features

Beef longissimus dorsi colour, marbling fat and surface texture are long established properties that are used in some countries by expert graders to classify beef carcasses, with subjective and inconsistent decision. As a computer vision system can deliver objective and consistent decisions rapidly and is capable of handling a greater variety of image features, attempts have been made to develop computerised predictions of eating quality based on these and other properties but have failed to adequately model the variation in eating quality. Therefore, in this study, examination of the ribeye at high magnification and consideration of a broad range of colour and marbling fat features was used to attempt to provide better information on beef eating quality. Wavelets were used to describe the image texture of the beef surface at high magnification rather than classical methods such as run lengths, difference histograms and co-occurrence matrices. Sensory panel and Instron analyses were performed on duplicate steaks to measure the quality of the beef. Using the classical statistical method of partial least squares regression (PLSR) it was possible to model a very high proportion of the variation in eating quality (r² = 0.88 for sensory overall acceptability and r² = 0.85 for 7-day WBS). Addition of non-linear texture terms to the models gave some improvements.     

Crispness level of potato chips affects temporal dynamics of flavor perception and mastication patterns in adults of different age groups

Little attention has been paid to the texture–flavor association in solid foods, especially crisp foods. This study aimed to determine whether crispness level affects temporal dynamics of perceived intensity of three types, i.e., plain, cheese, and spicy, of flavored potato chips with respect to three age groups: younger (20–25 years), middle-aged (40–45 years), and older (65+ years) adults. While eating potato chips, participants’ mastication pattern was also assessed by electromyography (EMG). Time–Intensity analysis showed that flavors were rated more intense and maximum flavor perception occurred quicker as crispness of potato chips increased. Overall, the effect of crispness level on flavor perception was more pronounced in the older participants. The average chew strength was greater in the crisper samples and regardless of flavor type the younger participants displayed shorter chew durations than older adults. A partial least squares regression demonstrated that mastication patterns, such as the number of chews, could well predict several key temporal flavor parameters such as the maximum intensity and the area under the curve in the middle age and older age groups. In conclusion, this study extends previous research showing that textural characteristics can influence flavor perception in liquid and soft foods to crisp/brittle foods. In addition, the effect of crispness level on flavor perception varies by flavor type, age group, and mastication pattern.     

Revisiting Fisher’s ‘Lady Tasting Tea’ from a perspective of sensory discrimination testing

The Lady Tasting Tea is a famous real story in the history of development of statistics, related to R.A. Fisher, one of the greatest statisticians and founders of modern statistics. The main learning and insight offered by this paper from revisiting the story are that the methodology of conventional sensory difference tests can be and should be expanded to cover the ‘M + N’ method with larger M and N. Unlike the conventional discrimination tests, which use multiple sets of ‘M + N’ samples with small M and N based on a binomial model, the ‘M + N’ tests with larger M and N can reach a statistical significance in a single trial using only one set of ‘M + N’ samples based on a hypergeometric distribution in Fisher’s exact test. This paper explores the applications of the new methods particularly in assessing performance of trained sensory panels and panelists. The connection of the odds ratio or common odds ratio with Cohen’s standardized mean difference d is also discussed.     

Effect of cryoprotectants,prebiotics and microencapsulation on survival of probiotic organisms in yoghurt and freeze-dried yoghurt

The survival of probiotic microorganisms including Lactobacillus acidophilus, Lactobacillus casei, Lactobacillus rhamnosus and Bifidobacterium spp. was evaluated in yoghurt and freeze-dried yoghurt after processing and storage. The effectiveness of microencapsulating probiotic organisms as well as adding cryoprotectants and prebiotics in improving their viability was also investigated. The viability of Bifidobacterium infantis 17930 and L. rhamnosus GG was reduced by 0.07 log, while that of L. casei 1520 and Bifidobacterium longum 1941 was reduced by 0.28 and 0.39 log, respectively. There was a 7% improvement in the viability of L. casei 1520 when cryoprotectant ‘Unipectine™ RS 150’ was added at 2.5% (w/v). The prebiotic ‘Raftilose^®P95’ when added at 1.5% w/v to yoghurt improved the viability of the combined selected probiotic organisms by 1.42 log during four weeks of storage at 4 °C. Microencapsulation with alginate improved viability of combined selected probiotic organisms by 0.31 log in freeze-dried yoghurt stored at 21 °C.     

Impact of pulsed light treatments on antioxidant characteristics and quality attributes of fresh-cut apples

The effects of pulsed light (PL) treatments combined with a quality-stabilizing dip on the quality and antioxidant attributes of fresh-cut ‘Golden delicious’ apples was studied. Apple wedges were dipped into a solution of 1% w/v N-acetylcysteine and 0.5% w/v CaCl₂ and flashed with broad-spectrum light with an overall radiant exposure of 4, 8, 12 and 16 J^.cm⁻². General microbial counts, colour, firmness, phenolic compounds and vitamin C contents were evaluated over 15 days at 5 °C. More pronounced reductions of the naturally-occurring microbiota were observed as the applied PL-dose increased. The quality-stabilizing pre-treatment effectively prevented browning phenomena on the cut-tissue surface. In addition, browning and oxidation were not promoted in PL flashed samples. Indeed, the initial contents in phenolic compounds and vitamin C were even better maintained than in untreated samples. Treatments of 8 and 16 J cm⁻² were most effective for maintaining the quality and antioxidant characteristics.Industrial relevancePulsed light technology is an emerging technique with good prospects for the decontamination of foods and food contact surfaces. Application of pulse light treatments for increasing safety and extending microbial shelf life of fresh-cut produce seems feasible. However, their effects on the quality and antioxidant characteristics of fruit need to be evaluated for successfully applying the technology at an industrial level.     

“Blown pack” Probabilistic Modeling for C. Algidicarnis and C. Estertheticum under the Effects of Storage Temperature,Vacuum Level and Package Shrink Temperature

A model for ‘blown pack’ probability (BPP) caused by spores of C.estertheticum DSM8809 and C.algidicarnis, was developed as a function of vacuum packaging variables: storage temperature(ST:-2, 2, 4 and 15 °C), vacuum level(VL:6 and 9mBar) and heat shrink temperature(HST:83 and 87 °C). Beef meat pieces, were inoculated with spore suspensions individually at 10²spores/cm², packed and daily monitored up to 90 days. The lower BPP, estimated by the log-logistic model, for C.algidicarnis was 0.8% at:-1.5 °C/6mBar/87 °C while for C.estertheticum was 99.13% at the same conditions. For both organisms, tested variables were unable to eliminate the risk of blown packaged spoilage, at 10²spores/cm² contamination level.