laboratory preparation and evaluation of pollock variety avocado (persea americana mill) guacamole

Journal of the Science of Food and Agriculture J Sci Food Agric 87:2068–2074 (2007)

Laboratory preparation and evaluationof Pollock variety avocado (Perseaamericana Mill) guacamoleGiselle A Ramtahal, John O Akingbala∗ and Gail SH Baccus-TaylorFood Science & Technology Unit, University of the West Indies, St Augustine, Trinidad

Abstract: Guacamole was produced from ripe avocado (Persea americana) by blending the pulp with local herbs,spices and salt. The guacamole was stored at 5 ◦C for 2 weeks, during which physical, chemical and microbialanalyses were conducted. Organoleptic evaluations by a semi-trained panel were also performed, until theguacamole was deemed unfit for human consumption. The results indicated that fresh avocado pulp contains 835,13, 16, 92, 44, 16 and 0.078 g kg−1, moisture, ash, protein, fat, carbohydrate, fiber, and vitamin C respectively,and has a pH of 6.7; compared with 838, 13, 16, 92, 44, 16, and 0.042 g kg−1, respectively, of the same nutrientsin freshly prepared guacamole, which has a pH of 6.0. During storage, the moisture content, consistency, totalsoluble solids and total titratable acidity (as citric acid) of the guacamole increased, but the vitamin C contentdecreased. The color of the avocado pulp, which darkened during conversion into guacamole, darkened furtheras storage increased as evidenced by a decrease in the L, a and b values. Sensory evaluation revealed that themean storage period (5 ◦C) for the guacamole was 6 days. Although the fresh avocado pulp, the freshly preparedguacamole, and the stored guacamole contained bacteria, yeasts and molds, the pathogens Staphylococcus aureusand Salmonella were absent. 2007 Society of Chemical Industry

Keywords: avocado guacamole; physical; chemical; microbiological; storage quality attributes

INTRODUCTIONThe avocado (Persea americana) is one of the importantcrops grown in Mexico, the United States of America(USA), the Dominican Republic, Brazil, Colombiaand the English-speaking Caribbean islands.1 The fruitis very popular in the Caribbean region where it hasbeen cultivated for many years. It is eaten as a freshfruit and as a salad component.1,2 The flesh is creamy,yellow–green to light yellow in color, richly flavoredand has a smooth, buttery consistency.1,2 Avocadoswhen purchased are usually very firm and have to beallowed to ripen before consumption. They do notripen on the tree.

In Trinidad and Tobago, and to a large extentof the Caribbean region, avocados have traditionallybeen marketed fresh and consumed principally asfresh fruit. Value-added products of the avocado fruitexist such as beverages and ice cream,2 althoughnone is manufactured in the region on a commercialbasis. Another value-added product is guacamole, aspiced puree prepared from the pulp of ripe avocados,blended with various herbs and spices for flavoring.2

The seasoned puree is used as a sandwich filling or asa ‘dip’ for crackers, potato chips or other snacks.2

This success of guacamole in other parts of theworld suggests that guacamole might also be consumeracceptable in the Caribbean region. Guacamole wouldutilize fairly large quantities of avocado, producing

a value-added item and increasing the utilization ofthe fruit in the region. The objective of this studywas to evaluate the physical, chemical, microbial andstorage quality of avocado guacamole that is sensoriallyacceptable to people of the Caribbean region.

EXPERIMENTALSelection and purchase of Avocados (Perseaamericana) and spicesMature avocado fruits (variety Pollock) were pur-chased from a local market. Onion powder, garlicpowder, ground black pepper, and table salt werepurchased from a local supermarket. Fresh Shadobeni (Eryngium foetidum) leaves, which were pur-chased from a local market, were washed with run-ning tap water, towel dried on paper towel andthen dried in a conventional forced air type ovenat 65 ◦C for approximately 12 h. The dried leaveswere blended (23 080 rad−1) in a Waring CommercialBlender (Dynamics Corp. of America, New Hartford,CT, USA) to obtain a powder.

MethodsPreliminary experimentsPreliminary experiments were carried out to determinean appropriate blending time for the guacamole, andto determine the most acceptable proportions of herbs

∗ Correspondence to: John O Akingbala, Food Science and Technology Unit, Department of Chemical Engineering, University of the West Indies,St. Augustine, TrinidadE-mail: [email protected](Received 13 May 2004; revised version received 30 January 2007; accepted 23 February 2007)Published online 8 June 2007; DOI: 10.1002/jsfa.2965

2007 Society of Chemical Industry. J Sci Food Agric 0022–5142/2007/$30.00

Preparation and quality of avocado guacamole

and spices to be added to the pulp. In determiningan acceptable blending time for the guacamole, freshavocado pulp (360 g) was blended at 23 080 rad−1

for 1, 4, 8 and 12 min, respectively, in a WaringCommercial Blender. Samples from the four blendingtimes were presented before a sensory panel of 10trained persons, students and staff of the Facultyof Engineering, University of the West Indies, whowere familiar with guacamole, to determine the mostacceptable blending time, using the sensory attributesof consistency and appearance.

The most acceptable proportion of herbs and spicesto be used in the guacamole was determined byblending each of three combinations of ingredientswith avocado pulp (360 g). The resultant guacamolefrom these combinations was presented before asensory panel of 10 persons who were very familiarwith guacamole, to determine the most acceptableproduct.

Preparation of guacamoleGuacamole was prepared according to Fig. 1. Avocadopulp (360 g per batch) was quartered and thenblended (at 23 080 rad−1) in a Waring CommercialBlender (Model 51BL30). Onion powder (1.2 g),garlic powder (0.86 g), shado beni powder (0.33 g),ground black pepper (0.50 g), salt (2 g), and lime(Citrus aurantifolia) juice (1.8 g) were properly mixedand then added into the pulp during blendingto produce guacamole. The guacamole was thenpackaged immediately in medium sized polyethyleneterephthalate (PET) containers (127 mm × 57.2 mm),and stored at refrigerated temperature (approx. 5 ◦C)for 2 weeks, for analysis.

AnalysesChemical analysisProximate composition of fresh avocado pulp andguacamole was determined according to AOACmethods:3 moisture (948.12), ash (900.02A), protein(955.04) and fat (920.30C). Fiber was determinedaccording to AOAC4 method 991.43. Ascorbic acidwas measured by the 2,6-dichlorophenolindophenolvisual titration method (AOAC Method 967.21).3

Approximately 10–20 mL of sample was made upto 100 mL with 3% metaphosphoric acid. The sampleplus acid were then filtered through Whatman 41 filterpaper. An aliquot (10 mL) of the metaphosphoricextract of the sample was then titrated with thestandard dye to a pink end-point.

Total titratable acidity was measured in termsof citric acid only, following the method describedby AOAC,3 because citric acid is the predominantacid in avocado.5 Pulped material (10 g) and water(100 mL) were boiled for 1 h, cooled, transferredto a 250 mL volumetric flask and filtered throughWhatman 41 filter paper. The filtrate (25 mL) wasthen titrated with 0.1 mol L−1 NaOH, using few dropsof phenolphthalein solution (1%) as the indicator.pH was measured using a digital Oakton pH meter

STORAGE

PACKAGING

GUACAMOLE

BLENDING

FORMULATION

MANUAL PEELING

SEED REMOVAL

WASHING

SELECTION

MATURE AVOCADO FRUIT

Figure 1. Flow chart for the production of avocado guacamole.

(Oakton pH/mV/◦C meter, 35 617-series; OaktonInstruments, Vernon Hills, IL, USA). The pH meterwas standardized using buffer solutions of pH 4and 7, respectively. The pH of finely blended (noadded water) avocado pulp was determined witha standard glass electrode at ambient temperature(25 ◦C).3 Total soluble solids was determined bya hand refractometer (Atago ATC-1E Brix 0–32%;Atago Company Limited, Itabashi-ku, Tokyo, Japan)(AOAC Method 932.12).3

Physical analysisConsistency (cm) was measured using a BostwickConsistometer (CSC Scientific Company Inc. Fairfax,VA, USA), at room temperature (25 ◦C). Color wasdetermined using a Minolta chroma meter (ModelCR-200b; Konica-Minolta, Ramsey, NJ, USA) onthe basis of three color values, namely L, a andb. L represents the lightness of the colors and islarger for light colors. Redness = +a; greenness = −a;yellowness = +b; while blueness = −b. A standard

J Sci Food Agric 87:2068–2074 (2007) 2069DOI: 10.1002/jsfa

GA Ramtahal, JO Akingbala, GS Baccus-Taylor

white calibration plate was used to calibrate thecolorimeter. The color system used was CIELAB,with the CIE notations 2◦ observer. Illuminant C wasused, where Y = 92.6; x = 0.3137 and y = 0.3209.The sample was placed in a clear plastic petri dishof 18 mm depth and covered with clear colorless(transparent) polyethylene before readings were takenat nine different locations on each sample. Infinitesolid was not determined for the samples. All analyseswere carried out in triplicate and duplicated threetimes (3 × 3 factorial).

Microbiological analysisMicrobiological analyses were carried out on the freshfruit and the guacamole, according to the methodsoutlined in Downes and Ito.6 Fresh avocado pulp andguacamole were analyzed for aerobes, yeasts, molds,lactic acid bacteria, and the pathogens Salmonella andStaphylococcus aureus. Each experiment was replicatedtwice and the average values reported.

Determination of microbial count. For the microbialcount, decimal dilutions of the food homogenatewere prepared. To determine total aerobes, 1 mL ofeach dilution was pipetted into separate, duplicate,appropriately marked petri dishes. Approximately12–15 mL of plate count agar (PCA) was then addedto each plate. The petri dishes were rotated to mixthe sample dilutions and agar medium. The agar wasallowed to solidify and then the plate was inverted.The plates were incubated at 32–35 ◦C for 24–48 h.To determine yeasts and molds, 1 mL of each dilutionwas plated unto acidified (1% tartaric acid) potatodextrose agar (PDA) and incubated at 28 ◦C for24–48 h. From the decimal dilutions, pour overlayplates were prepared using DeMan Rogosa Sharpeagar (MRS) to determine lactic acid bacteria. Theplates were incubated at 35–37 ◦C for 48–72 h.

Detection of Staphylococcus aureus. Tubes of trypti-case soy broth containing 10% sodium chloride wereinoculated with a 1 mL aliquot of the sample for thedetection of Staphylococcus aureus. The tubes wereincubated at 32–35 ◦C for 45–48 h (enrichment step).From the enrichment broth spread plates were pre-pared using Baird Parker agar (BPA) enriched withegg tellurite emulsion. The plates were incubated at35–37 ◦C for 24–48 h. Typical colonies are shiny,black, convex and 1.0–1.5 mm in diameter.6

Detection of Salmonella. A 25 g sample of pulpor guacamole was homogenized in 225 mL oftetrathionate (TT) broth for 1 min (enrichment step).The TT broth was then incubated at 35 ◦C for24 ± 2 h. Loopfuls (3 mm) of the incubated TT brothwas streaked on xylose lysine desoxycholate (XLD)agar, and hektoen enteric (HE) agar.6 The plates werethen incubated at 35 ◦C for 24 ± 2 h and examined forthe presence of colonies suspected to be Salmonella,which are blue–green to blue colonies with or without

black centers on XLD agar, or pink colonies withor without black centers on HE agar. All reagentsused in chemical and microbiological analyses were ofanalytical grade.

Sensory analysisSensory evaluation was conducted to determine thebest mix of herbs and spices to be added to the pureein order to obtain an acceptable guacamole, and todetermine acceptability of the stored product. Storedsamples were evaluated for general appearance, color,aroma, consistency, taste and overall acceptability,using a five-point hedonic scale, where 1 was‘like extremely’, and 5 was ‘dislike extremely’.7

The evaluations, which began at mid-morning andended at mid-afternoon, were conducted in an air-conditioned (20–25 ◦C) room, away from noise andodors. The room was well lit to permit adequateviewing while minimizing distraction, and containedseparate entrance and exit areas. It was partitioned intoindividual cubicles to prevent unwanted exchange bypanelists and to encourage independent judgment.

Preparation of samplesControlled preparation of products was carried out.The samples were served in styrotex (sanitary) plates.Each panelist received about 15 g of paste on a salt-freecracker. Samples assigned random three-digit codenumbers, were served at a temperature of 4–10 ◦C.The panelists were provided with taste-neutral waterfor oral rinsing between samples.

Selection and preparation of panelistsTen semi-trained panelists already familiar with gua-camole were selected to conduct the sensory eval-uation. They included students and staff mem-bers of the Food Science and Technology Unit.The terms appearing on the sensory evaluationform/questionnaire were explained to each panelistbefore he/she completed the form.

Statistical analysisMeans were calculated by one-way analysis of variance(ANOVA), and separated using t-test or Duncan’s newmultiple-range test where appropriate.8

RESULTS AND DISCUSSIONPreliminary experimentsDetermination of appropriate blending time for guacamoleTable 1 shows the mean sensory scores for thedetermination of an appropriate blending time forguacamole. The consistency of guacamole blended for1 min was coarse, while that blended for 12 min waswatery. Blending for 4 and 8 min produced guacamoleof similar consistency that was acceptable by the panel.However, the sensory score for general appearance ofthe guacamole blended for 8 min was significantlybetter than that blended for 4 min. Therefore avocado

2070 J Sci Food Agric 87:2068–2074 (2007)DOI: 10.1002/jsfa


pulp was blended for 8 min in the preparation ofguacamole. Also of the three mixtures of ingredients(Table 2), the sensory scores of mixture A (1.2) weresignificantly (P = 0.05) better than the scores formixtures B (2.5) and C (3.7). Sample C was theleast preferred because it was bland, while the panelcommented that the flavors of onion and garlic weretoo strong in sample B. This indicates that thoughgarlic and onion are preferred flavor ingredients inCaribbean foods, there is an upper limit to theirinclusion in the foods for acceptance by the consumer.Lime juice was added to the mixture to flavor theguacamole and to lower the pH. A low pH preventsthe rapid growth of micro-organisms, stabilizes vitaminC against excessive breakdown, and should preventexcessive darkening of guacamole color. Also theadded lime juice was high in ascorbic acid, which couldsupplement the ascorbic acid content of guacamole.

Proximate composition of fresh avocado pulp andguacamoleThe proximate composition and vitamin C contentof avocado pulp and freshly prepared guacamole arepresented in Table 3. The composition of avocadopulp in this study was comparable to values reportedby Nakasone and Paull.5 The guacamole was notsignificantly different (P = 0.05) from the avocadopulp for moisture, ash, protein, fat, carbohydrateand fiber. However, the vitamin C content of theguacamole was significantly lower compared with thatof the avocado pulp, even though lime juice addedto the guacamole, could have increased its vitamin Ccontent. The lower vitamin C content of guacamolecould be as a result of the exposure of the pulp toair during blending, which resulted in oxidation ofthe vitamin. Vitamin C is highly unstable and is

Table 1. Mean sensory scores for the determination of an appropriate

blending time for guacamole

Sensory attribute

Blending time (min) Consistency General appearance

1 3.1a 3.8a

4 1.8b 2.0c

8 1.4b 1.4d

12 2.8a 2.9b

Means with the same letter within a column are not significantlydifferent (P ≤ 0.05).Values are the means of ten replicates.

Table 2. Blends of ingredients used for flavoring guacamole

Combinations used

Flavoring ingredient A (g) B (g) C (g)

Salt 2.0 3.0 1.0Garlic powder 0.86 1.42 0.3Shado beni 0.33 0.55 0.15Onion powder 1.2 2.0 0.5Ground black pepper 0.50 0.50 0.50

easily destroyed by oxidation, exposure to light orhigh temperature.9 The incorporation of air into thepulp during finishing, blending and container fillinghas long been recognized as cause of vitamin C lossduring processing.10

Physical and chemical characterization of freshavocado pulp and freshly prepared guacamoleThe physical and chemical characteristics of avocadopulp and avocado guacamole are presented inTable 4. Guacamole could be classified as a minimallyprocessed food since it was not heat treated, containshigh moisture (838 g kg−1), and the compositionwas not significantly altered from that of thebasic ingredient.11 The pH of the guacamole wassignificantly (P = 0.05) lowered to 6.0 from the initialpH of 6.7 of the pulp, by the addition of lime juice(1.8 g). Total titratable acid (as citric acid) of theavocado pulp and avocado guacamole was 0.0011 gkg−1 and 0.0014 g kg−1, respectively, with some ofthe increase in acidity derived from the added limejuice. Total soluble solids was 9.2◦Brix for the pulpand 10.5◦Brix for the guacamole. This increase in thetotal soluble solids could be as a result of enzymaticand acid breakdown of insoluble carbohydrate intosoluble sugars during processing of guacamole.12 Theconsistency of avocado guacamole was 0.5 cm. Thetotal titratable acid, pH, total soluble solids and color

Table 3. Composition1 of fresh avocado pulp and guacamole (g kg−1)

Avocado pulp

Composition This study Literature2 Guacamole

Moisture 835a 828 838a

Ash 13a 8 13a

Protein 16a 15 16a

Fat 92a 93 92a

Carbohydrate3 44a 57 44a

Fiber 16a 16 16a

Vitamin C 7.8a – 4.2b

1 Mean of three observations; means not followed by the same letterson a row are significantly different (P ≤ 0.05).2 Nakasone and Paull.53 By difference.

Table 4. Mean physical and chemical properties of fresh avocado

pulp and guacamole

Parameter Avocado pulp Guacamole

Moisture (g kg−1) 835a 838a

Total titratable acid (g kg−1) 0.0011a 0.0014b

pH 6.7a 6.0b

Total soluble solids (◦Brix) 9.2a 10.5b

Consistency (cm) – 0.5Color

L 73.4 61.7b

a −1.7a −7.9b

b 43.7a 30.0b

Values are the means of three replicates.Means in a row not followed by the same letters are different (P ≤ 0.05)



were significantly (P = 0.05) different between theguacamole and avocado pulp. With respect to color,the L and b values were lower for the guacamolecompared with the avocado pulp. This, apparently,was due to enzyme browning reactions as a result ofthe incorporation of oxygen during blending togetherof the pulp and the spices. Lime juice was added tothe mixture to reduce the expected darkening of thecolors due to oxidation of the polyphenols present inthe pulp by the introduced air. However, this may havenot been effective enough to prevent the lowering ofthe L and b values significantly (P = 0.05).

Effect of storage on composition and qualitycharacteristics of guacamoleMoisture contentThere was significant (P = 0.05) increase in the mois-ture content of guacamole during storage (Table 5).This increase in the moisture content probably asa result of acid and enzymatic hydrolysis of thepulp increased the mobility (reduced the viscosity)of guacamole and may support the growth of micro-organisms.13,14

Total soluble solidsThe total soluble solids of the guacamole increasedduring storage from 10.5◦Brix on day 1 to 12.0◦Brixon day 14 of storage due to increase in total acid,and due to the activities of polygalacturonase andα- and β-galactosidase enzymes which hydrolyzedthe carbohydrate and cell wall components intosimpler, lower molecular weight compounds, whichwere more water soluble.12–14 Since the avocadofruit is rich in oil, which is liable to break downto fatty acids and glycerol in the presence ofmoisture, micro-organisms and enzymes,9 the increasein acidity was partly as a result of fat hydrolysisinto free fatty acids. Fermentation of the fermentablecarbohydrates in guacamole also contributed toincreased acidity and breakdown of carbohydrates.Added to acid breakdown of carbohydrates is theenzymatic hydrolysis of cellulose by the celluloseenzyme, all of which reduce complex carbohydratesinto simpler forms, reducing viscosity of the guacamoleduring storage.12 The enzyme hydrolysis, which results

in the softening of avocado mesocarp and increasedconcentration of lower molecular weight compounds,is increased by the long exposure of the pulp toethylene present in the mixture.12

Ascorbic acid (vitamin C)Vitamin C content of the guacamole decreasedsignificantly (P = 0.05) during storage. There wasa 14% decrease of vitamin C on day 2, whichdecreased a further 60% by day 14 of storage. Ascorbicacid is easily destroyed by oxidation, catalysed byoxidases contained within the cells of the fruit, andreleased during blending of the pulp.10 Furthermorethe incorporation of air into the guacamole duringblending and container filling, and the incidence oflight on the product are possible causes of the vitaminC loss.10

ColorThe L value, which is a measure of lightness ofcolor, decreased with increasing storage, revealing adarkening of the avocado guacamole probably dueto enzymatic browning (Table 6). Recent reportscredited the activities of the polyphenolic oxidaseenzymes catecol oxidase, laccase, and phloroglucinoloxidase enzymes as being responsible for the browningof vegetables.16 Catecol oxidase oxidizes o-diphenolsto quinines and hydroxylates monophenols to o-diphenols; laccase oxidizes both o- and p-diphenols,

Table 6. Color of guacamole during refrigerated storage (5 ◦C)

Color value

Storage period (days) L a b

0 61.7 −7.9 30.02 60.8b −6.9b 28.6b

4 59.1c −5.3c 25.4c

6 57.9d −4.3d 23.5d

8 56.2e −4.0e 22.4e

10 55.7f −3.2f 21.9f

12 55.3g −3.1f 21.2g

14 54.8h −1.6g 18.4h

Values are means of three replicates.Means with the same letter within a column are not significantlydifferent (P ≤ 0.05).

Table 5. Mean physical and chemical properties of guacamole during refrigerated storage at (5 ◦C)

Storageperiod (days)

Moisture(g kg−1)

Consistency(cm)

Total solublesolids (◦Brix)

Total titrableacid (g kg−1) pH

Vitamin C(mg kg−1)

0 838d 0.5g 10.5d 0.0014f 6.0a 42a

2 820e 0.5g 11.5c 0.0028e 4.9b 36b

4 839d 0.6f 11.5c 0.0030d 4.9b 29c

6 844d 0.9e 11.7abc 0.0031d 4.8c 23d

8 853c 1.0d 11.8abc 0.0033c 4.6d 18e

10 863b 1.2c 11.9ab 0.0034bc 4.6d 14f

12 872a 1.4b 12.0a 0.0035b 4.5e 12g

14 878a 1.5a 12.0a 0.0037a 4.4f 11g

Values are the means of three replicates.Means with the same letter within a column are not significantly different (P ≤ 0.05).



and the three enzymes including phloroglucinol,catalyze the oxidation of phenols to brown pigments.15

The substrate oxidized most readily by these enzymeswas nordihydroguaiaretic acid, followed by catecholand catechin. The browning caused by these enzymesmay have been intensified during storage of theguacamole at 5 ◦C possibly by ethylene present inthe pulp;16 and by the pH of the guacamole duringthe 14 days of storage (4.4–4.9), which was closeto the optimum pH (4.8) for avocado polyphenolaseactivity.17 As the storage time increased, the a valuesof the guacamole decreased, indicating a reductionin the greenness of the guacamole. The green colorof guacamole is due to the presence of chlorophyll,which is a magnesium organic complex.18 Changesin pH, especially at the acidic pH of guacamole(4.4–4.9) may cause degradation of chlorophyll, firstto a dull olive green color of pheophytin, and later to abrown pigment (pheophorbide) formed upon furtherdegradation.18

The decrease in the b values of the guacamole duringstorage indicated a reduction in the yellowness of theproduct, which can be attributed to the darkening ofthe color of the product due to enzyme browning andincrease in the breakdown products of chlorophyll.

Sensory evaluation of guacamoleColor, aroma, consistency, taste and overall accept-ability of freshly prepared and stored guacamole arepresented in Table 7. The mean scores for generalappearance, color, aroma, consistency, and taste offresh avocado guacamole (day 0) were 1.1, 1.2, 1.4,1.3 and 1.1, respectively, which indicated that the freshguacamole was very much liked. On day 2 of storage,there was no significant difference between the sen-sory parameters of the fresh guacamole. However,from day 4 onwards, there was a significant increase inthe mean scores of the sensory parameters, which werestill acceptable on day 6 of storage. The sensory evalu-ation was interrupted on day 8 of storage because theguacamole was no longer consumer acceptable. Themean sensory scores for color increased with increas-ing storage in consonance with the darkening observedby the color measurements. The taste and aroma of theguacamole also deteriorated during storage (Table 7)most likely due to off-flavor of the free fatty acids of

Table 7. Mean scores for sensory attributes of guacamole

Sensory attributeStorageperiod(days)

Generalappearance Color Aroma Consistency Taste

0 1.1d 1.2c 1.4d 1.3c 1.1c

2 1.1d 1.2c 1.4d 1.3c 1.1c

4 1.5c 1.4c 1.9c 1.5c 1.4c

6 2.0b 2.0b 2.5b 2.1b 2.3b

8 4.0a 4.6a 4.3a 4.0a 4.2a

Means with same letter within a column are not significantly different(P ≤ 0.05)Values are the means of ten replicates.

hydrolyzed fat and the off-flavor from oxidized phenolcompounds.15 As the storage period increased, thechange in color and the softening of the guacamoleresulted in marked (P ≤ 0.05) increases in sensoryscores (declining quality) for general appearance.

Microbial evaluationFresh avocado pulpCounts of aerobes, yeasts, and lactic acid bac-teria of avocado pulp were 8 × 102 CFU g−1,8 × 102 CFU g−1, and 3 × 101 CFU g−1 respectively(Table 8). The high pH (6.7), high moisture content,and readily available nutrients of fresh avocado pulpsupported microbial growth. However, the pathogensStaphylococcus aureus usually found on humans, andSalmonella, sometimes found on fruits, utensils andspices, were absent, an indication of adherence togood sanitation practices during the preparation ofavocado guacamole.

Fresh and stored guacamoleCounts of aerobes, yeasts and molds, lactic acidbacteria, and the detection of selected pathogensStaphylococcus aureus and Salmonella, in fresh gua-camole (day 0) and in refrigerated (5 ◦C) storedguacamole are presented on Table 9. The counts ofaerobes (2 × 103 CFU g−1), yeasts (1 × 103 CFU g−1),and lactic acid bacteria (4 × 102 CFU g−1) were lowand must have been incident on the fruit (Table 8).The low initial counts are important in the produc-tion of guacamole since heat, which causes fast flavorand color degradation of avocado19 cannot be appliedin the production of guacamole for reducing highbacteria load, and cold storage of the pulp resultsin texture, flavor and color problems. The microbialcounts, which remained relatively low until day 10of storage when the experiment was stopped, weredue to low initial numbers of micro-organisms, andpossibly due to bacteriostatic and bacteriocidal effectsof some of the spices used for flavoring. Molds werepresent in the guacamole, but Staphylococcus aureusand Salmonella were absent, reflecting proper hygienichandling, production and storage.

CONCLUSIONA good quality sensory acceptable guacamole wasproduced by blending together ripe avocado (Pollack

Table 8. Microbial counts of fresh avocado pulp

Fresh avocado pulp

Type of micro-organism Number of cfu g−1 log(cfu g−1)

Aerobes 8 × 102 2.90Yeast 8 × 102 2.90Mold Present –Lactic acid bacteria 3 × 101 1.48Staphylococcus aureus Absent –Salmonella Absent –



Table 9. Microbial counts of fresh guacamole (day 0) and stored

guacamole (day 10) at 5 ◦C

Guacamole

Type ofmicro-organism

Time(days)

Number ofcfu g−1

log(cfu g−1)

Aerobes 0 2 × 103 3.302 8 × 103 3.904 1 × 104 4.006 3 × 104 4.488 6 × 104 4.78

10 7 × 104 4.85

Yeasts 0 1 × 103 3.002 2 × 103 3.304 9 × 103 3.956 2 × 104 4.308 6 × 104 4.78

10 7 × 104 4.85

Lactic acid bacteria 0 4 × 102 2.62 8 × 102 2.904 2 × 103 3.306 8 × 103 3.908 3 × 104 4.48

10 4 × 104 4.60

Molds 0 Present –2 Present –4 Present –6 Present –8 Present –

10 Present –

Salmonella and 0 Absent –Stapylococcus aureus 2 Absent –

4 Absent –6 Absent –8 Absent –

10 Absent –

variety) pulp, local herbs and spices and lime juice.The guacamole, though bacteriologically safe, retainedacceptable sensory quality for 6 days only, which is tooshort a storage period for a large-scale production ofguacamole to be economically viable or attractive. Itis therefore essential to study the mechanism for thespoilage of avocado guacamole under storage, so as todevise methods to increase the shelf life of the product.

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laboratory preparation and evaluation of pollock variety avocado (persea americana mill) guacamole

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